diff --git a/crates/qmd-syntax-helper/src/conversions/div_whitespace.rs b/crates/qmd-syntax-helper/src/conversions/div_whitespace.rs
index c8119a4..03c47aa 100644
--- a/crates/qmd-syntax-helper/src/conversions/div_whitespace.rs
+++ b/crates/qmd-syntax-helper/src/conversions/div_whitespace.rs
@@ -72,7 +72,21 @@ impl DivWhitespaceConverter {
             let error_row = error
                 .location
                 .as_ref()
-                .map(|loc| loc.range.start.row)
+                .and_then(|loc| {
+                    // Get the start offset from SourceInfo
+                    let offset = loc.start_offset();
+                    // Binary search to find which line this offset is on
+                    match line_starts.binary_search(&offset) {
+                        Ok(idx) => Some(idx),
+                        Err(idx) => {
+                            if idx > 0 {
+                                Some(idx - 1)
+                            } else {
+                                Some(0)
+                            }
+                        }
+                    }
+                })
                 .unwrap_or(0);
 
             // The error might be on the line itself or the line before (for div fences)
diff --git a/crates/quarto-error-reporting/src/diagnostic.rs b/crates/quarto-error-reporting/src/diagnostic.rs
index ab2b1fd..6b8d808 100644
--- a/crates/quarto-error-reporting/src/diagnostic.rs
+++ b/crates/quarto-error-reporting/src/diagnostic.rs
@@ -345,7 +345,7 @@ impl DiagnosticMessage {
             if let Some(loc) = &self.location {
                 // Try to map with context if available
                 if let Some(ctx) = ctx {
-                    if let Some(mapped) = loc.map_offset(loc.range.start.offset, ctx) {
+                    if let Some(mapped) = loc.map_offset(loc.start_offset(), ctx) {
                         if let Some(file) = ctx.get_file(mapped.file_id) {
                             write!(
                                 result,
@@ -359,13 +359,9 @@ impl DiagnosticMessage {
                     }
                 } else {
                     // No context: show immediate location (1-indexed for display)
-                    write!(
-                        result,
-                        "  at {}:{}\n",
-                        loc.range.start.row + 1,
-                        loc.range.start.column + 1
-                    )
-                    .unwrap();
+                    // Note: Without context, we can't get row/column from offsets
+                    // We could map_offset with ctx to get Location, but ctx is None here
+                    write!(result, "  at offset {}\n", loc.start_offset()).unwrap();
                 }
             }
 
@@ -500,15 +496,12 @@ impl DiagnosticMessage {
     fn extract_file_id(
         source_info: &quarto_source_map::SourceInfo,
     ) -> Option<quarto_source_map::FileId> {
-        match &source_info.mapping {
-            quarto_source_map::SourceMapping::Original { file_id } => Some(*file_id),
-            quarto_source_map::SourceMapping::Substring { parent, .. } => {
+        match source_info {
+            quarto_source_map::SourceInfo::Original { file_id, .. } => Some(*file_id),
+            quarto_source_map::SourceInfo::Substring { parent, .. } => {
                 Self::extract_file_id(parent)
             }
-            quarto_source_map::SourceMapping::Transformed { parent, .. } => {
-                Self::extract_file_id(parent)
-            }
-            quarto_source_map::SourceMapping::Concat { pieces } => {
+            quarto_source_map::SourceInfo::Concat { pieces } => {
                 // For concatenated sources, use the first piece's file_id
                 pieces
                     .first()
@@ -544,8 +537,9 @@ impl DiagnosticMessage {
         };
 
         // Map the location offsets back to original file positions
-        let start_mapped = main_location.map_offset(main_location.range.start.offset, ctx)?;
-        let end_mapped = main_location.map_offset(main_location.range.end.offset, ctx)?;
+        // map_offset expects relative offsets (0 = start of this SourceInfo's range)
+        let start_mapped = main_location.map_offset(0, ctx)?;
+        let end_mapped = main_location.map_offset(main_location.length(), ctx)?;
 
         // Determine report kind and color
         let (report_kind, main_color) = match self.kind {
@@ -591,9 +585,10 @@ impl DiagnosticMessage {
 
                 if detail_file_id == file_id {
                     // Map detail offsets to original file positions
+                    // map_offset expects relative offsets (0 = start of SourceInfo's range)
                     if let (Some(detail_start), Some(detail_end)) = (
-                        detail_loc.map_offset(detail_loc.range.start.offset, ctx),
-                        detail_loc.map_offset(detail_loc.range.end.offset, ctx),
+                        detail_loc.map_offset(0, ctx),
+                        detail_loc.map_offset(detail_loc.length(), ctx),
                     ) {
                         let detail_span = detail_start.location.offset..detail_end.location.offset;
                         let detail_color = match detail.kind {
@@ -787,22 +782,9 @@ mod tests {
     fn test_location_in_to_text_without_context() {
         use crate::builder::DiagnosticMessageBuilder;
 
-        // Create a location at row 10, column 5
-        let location = quarto_source_map::SourceInfo::original(
-            quarto_source_map::FileId(0),
-            quarto_source_map::Range {
-                start: quarto_source_map::Location {
-                    offset: 100,
-                    row: 10,
-                    column: 5,
-                },
-                end: quarto_source_map::Location {
-                    offset: 110,
-                    row: 10,
-                    column: 15,
-                },
-            },
-        );
+        // Create a location at offsets 100-110
+        let location =
+            quarto_source_map::SourceInfo::original(quarto_source_map::FileId(0), 100, 110);
 
         let msg = DiagnosticMessageBuilder::error("Invalid syntax")
             .with_location(location)
@@ -810,9 +792,9 @@ mod tests {
 
         let text = msg.to_text(None);
 
-        // Without context, should show immediate location (1-indexed)
+        // Without context, should show offset (we can't get row/column without context)
         assert!(text.contains("Invalid syntax"));
-        assert!(text.contains("at 11:6")); // row 10 + 1, column 5 + 1
+        assert!(text.contains("at offset 100"));
     }
 
     #[test]
@@ -826,21 +808,10 @@ mod tests {
             Some("line 1\nline 2\nline 3\nline 4".to_string()),
         );
 
-        // Create a location in that file
+        // Create a location in that file (offset 7 is start of "line 2")
         let location = quarto_source_map::SourceInfo::original(
-            file_id,
-            quarto_source_map::Range {
-                start: quarto_source_map::Location {
-                    offset: 7, // Start of "line 2"
-                    row: 1,
-                    column: 0,
-                },
-                end: quarto_source_map::Location {
-                    offset: 13,
-                    row: 1,
-                    column: 6,
-                },
-            },
+            file_id, 7,  // Start of "line 2"
+            13, // End of "line 2"
         );
 
         let msg = DiagnosticMessageBuilder::error("Invalid syntax")
@@ -859,21 +830,8 @@ mod tests {
     fn test_location_in_to_json() {
         use crate::builder::DiagnosticMessageBuilder;
 
-        let location = quarto_source_map::SourceInfo::original(
-            quarto_source_map::FileId(0),
-            quarto_source_map::Range {
-                start: quarto_source_map::Location {
-                    offset: 100,
-                    row: 10,
-                    column: 5,
-                },
-                end: quarto_source_map::Location {
-                    offset: 110,
-                    row: 10,
-                    column: 15,
-                },
-            },
-        );
+        let location =
+            quarto_source_map::SourceInfo::original(quarto_source_map::FileId(0), 100, 110);
 
         let msg = DiagnosticMessageBuilder::error("Invalid syntax")
             .with_location(location)
@@ -881,19 +839,16 @@ mod tests {
 
         let json = msg.to_json();
 
-        // Should have location field with range info
+        // Should have location field with Original variant
         assert!(json.get("location").is_some());
         let loc = &json["location"];
-        assert!(loc.get("range").is_some());
-
-        // Verify the range is serialized correctly
-        let range = &loc["range"];
-        assert_eq!(range["start"]["row"], 10);
-        assert_eq!(range["start"]["column"], 5);
-        assert_eq!(range["start"]["offset"], 100);
-        assert_eq!(range["end"]["row"], 10);
-        assert_eq!(range["end"]["column"], 15);
-        assert_eq!(range["end"]["offset"], 110);
+
+        // Verify the SourceInfo is serialized correctly (as Original enum variant)
+        assert!(loc.get("Original").is_some());
+        let original = &loc["Original"];
+        assert_eq!(original["file_id"], 0);
+        assert_eq!(original["start_offset"], 100);
+        assert_eq!(original["end_offset"], 110);
     }
 
     #[test]
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/inline.rs b/crates/quarto-markdown-pandoc/src/pandoc/inline.rs
index 3fbfd90..e8d939d 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/inline.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/inline.rs
@@ -484,7 +484,7 @@ mod tests {
     use super::*;
 
     fn dummy_source_info() -> quarto_source_map::SourceInfo {
-        quarto_source_map::SourceInfo::original(
+        quarto_source_map::SourceInfo::from_range(
             quarto_source_map::FileId(0),
             quarto_source_map::Range {
                 start: quarto_source_map::Location {
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/location.rs b/crates/quarto-markdown-pandoc/src/pandoc/location.rs
index 18c4cf5..25047b1 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/location.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/location.rs
@@ -63,6 +63,16 @@ impl SourceInfo {
         }
     }
 
+    /// Get the start offset
+    pub fn start_offset(&self) -> usize {
+        self.range.start.offset
+    }
+
+    /// Get the end offset
+    pub fn end_offset(&self) -> usize {
+        self.range.end.offset
+    }
+
     /// Convert to quarto-source-map::SourceInfo (temporary conversion helper)
     ///
     /// This helper bridges between pandoc::location types and quarto-source-map types.
@@ -71,7 +81,7 @@ impl SourceInfo {
     /// Creates an Original mapping with a dummy FileId(0).
     /// For proper filename support, use to_source_map_info_with_mapping with a real FileId.
     pub fn to_source_map_info(&self) -> quarto_source_map::SourceInfo {
-        quarto_source_map::SourceInfo::original(
+        quarto_source_map::SourceInfo::from_range(
             quarto_source_map::FileId(0),
             quarto_source_map::Range {
                 start: quarto_source_map::Location {
@@ -96,7 +106,7 @@ impl SourceInfo {
         &self,
         file_id: quarto_source_map::FileId,
     ) -> quarto_source_map::SourceInfo {
-        quarto_source_map::SourceInfo::original(
+        quarto_source_map::SourceInfo::from_range(
             file_id,
             quarto_source_map::Range {
                 start: quarto_source_map::Location {
@@ -132,14 +142,14 @@ pub fn node_location(node: &tree_sitter::Node) -> quarto_source_map::Range {
 }
 
 pub fn node_source_info(node: &tree_sitter::Node) -> quarto_source_map::SourceInfo {
-    quarto_source_map::SourceInfo::original(quarto_source_map::FileId(0), node_location(node))
+    quarto_source_map::SourceInfo::from_range(quarto_source_map::FileId(0), node_location(node))
 }
 
 pub fn node_source_info_with_context(
     node: &tree_sitter::Node,
     context: &ASTContext,
 ) -> quarto_source_map::SourceInfo {
-    quarto_source_map::SourceInfo::original(context.current_file_id(), node_location(node))
+    quarto_source_map::SourceInfo::from_range(context.current_file_id(), node_location(node))
 }
 
 pub fn empty_range() -> Range {
@@ -158,7 +168,7 @@ pub fn empty_range() -> Range {
 }
 
 pub fn empty_source_info() -> quarto_source_map::SourceInfo {
-    quarto_source_map::SourceInfo::original(
+    quarto_source_map::SourceInfo::from_range(
         quarto_source_map::FileId(0),
         quarto_source_map::Range {
             start: quarto_source_map::Location {
@@ -177,15 +187,10 @@ pub fn empty_source_info() -> quarto_source_map::SourceInfo {
 
 /// Extract filename index from quarto_source_map::SourceInfo by walking to Original mapping
 pub fn extract_filename_index(info: &quarto_source_map::SourceInfo) -> Option<usize> {
-    match &info.mapping {
-        quarto_source_map::SourceMapping::Original { file_id } => Some(file_id.0),
-        quarto_source_map::SourceMapping::Substring { parent, .. } => {
-            extract_filename_index(parent)
-        }
-        quarto_source_map::SourceMapping::Transformed { parent, .. } => {
-            extract_filename_index(parent)
-        }
-        quarto_source_map::SourceMapping::Concat { pieces } => {
+    match info {
+        quarto_source_map::SourceInfo::Original { file_id, .. } => Some(file_id.0),
+        quarto_source_map::SourceInfo::Substring { parent, .. } => extract_filename_index(parent),
+        quarto_source_map::SourceInfo::Concat { pieces } => {
             // Return first non-None filename_index from pieces
             pieces
                 .iter()
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/source_map_compat.rs b/crates/quarto-markdown-pandoc/src/pandoc/source_map_compat.rs
index 4104c7f..323e018 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/source_map_compat.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/source_map_compat.rs
@@ -29,7 +29,7 @@ pub fn node_to_source_info(node: &Node, file_id: FileId) -> SourceInfo {
     let start_pos = node.start_position();
     let end_pos = node.end_position();
 
-    SourceInfo::original(
+    SourceInfo::from_range(
         file_id,
         Range {
             start: Location {
@@ -91,16 +91,16 @@ pub fn old_to_new_source_info(
     };
 
     // Convert the Range (both use the same Location structure)
-    SourceInfo::original(
+    SourceInfo::from_range(
         file_id,
         Range {
             start: Location {
-                offset: old_info.range.start.offset,
+                offset: old_info.start_offset(),
                 row: old_info.range.start.row,
                 column: old_info.range.start.column,
             },
             end: Location {
-                offset: old_info.range.end.offset,
+                offset: old_info.end_offset(),
                 row: old_info.range.end.row,
                 column: old_info.range.end.column,
             },
@@ -108,6 +108,44 @@ pub fn old_to_new_source_info(
     )
 }
 
+/// Convert quarto-source-map::SourceInfo to a quarto_source_map::Range, with a fallback if mapping fails.
+///
+/// This is for use with PandocNativeIntermediate which uses quarto_source_map::Range.
+/// Provides a fallback Range with zero row/column values if the mapping fails.
+///
+/// # Arguments
+/// * `source_info` - The SourceInfo to convert
+/// * `ctx` - The ASTContext containing the source context
+///
+/// # Returns
+/// A quarto_source_map::Range with row/column information if available, or a Range with offsets only
+pub fn source_info_to_qsm_range_or_fallback(
+    source_info: &SourceInfo,
+    ctx: &ASTContext,
+) -> quarto_source_map::Range {
+    let start_mapped = source_info.map_offset(0, &ctx.source_context);
+    let end_mapped = source_info.map_offset(source_info.length(), &ctx.source_context);
+
+    match (start_mapped, end_mapped) {
+        (Some(start), Some(end)) => quarto_source_map::Range {
+            start: start.location,
+            end: end.location,
+        },
+        _ => quarto_source_map::Range {
+            start: quarto_source_map::Location {
+                offset: source_info.start_offset(),
+                row: 0,
+                column: 0,
+            },
+            end: quarto_source_map::Location {
+                offset: source_info.end_offset(),
+                row: 0,
+                column: 0,
+            },
+        },
+    }
+}
+
 // Note: Tests for these functions will be validated through integration tests
 // when they're used in actual parsing modules. The tree-sitter-qmd parser
 // setup is too complex to mock in unit tests here.
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter.rs
index b2f926e..26be6f6 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter.rs
@@ -103,7 +103,7 @@ fn process_list(
     //     but the next item might not itself be a paragraph.
 
     let mut has_loose_item = false;
-    let mut last_para_range: Option<quarto_source_map::Range> = None;
+    let mut last_para_end_row: Option<usize> = None;
     let mut last_item_end_row: Option<usize> = None;
     let mut list_items: Vec<Blocks> = Vec::new();
     let mut is_ordered_list: Option<ListAttributes> = None;
@@ -153,9 +153,9 @@ fn process_list(
             }
         }
 
-        // is the last item loose? Check the last paragraph range
-        if let Some(ref last_range) = last_para_range {
-            if last_range.end.row != child_range.start.row {
+        // is the last item loose? Check the last paragraph end row
+        if let Some(last_para_end) = last_para_end_row {
+            if last_para_end != child_range.start.row {
                 // if the last paragraph ends on a different line than the current item starts,
                 // then the last item was loose, mark it
                 has_loose_item = true;
@@ -186,12 +186,15 @@ fn process_list(
             has_loose_item = true;
 
             // technically, we don't need to worry about
-            // last paragraph range after setting has_loose_item,
+            // last paragraph end row after setting has_loose_item,
             // but we do it in case we want to use it later
-            last_para_range = None;
-            last_item_end_row = blocks
-                .last()
-                .map(|b| get_block_source_info(b).range.end.row);
+            last_para_end_row = None;
+            last_item_end_row = blocks.last().and_then(|b| {
+                let source_info = get_block_source_info(b);
+                source_info
+                    .map_offset(source_info.length(), &context.source_context)
+                    .map(|mapped| mapped.location.row)
+            });
             list_items.push(blocks);
             continue;
         }
@@ -199,22 +202,28 @@ fn process_list(
         // is this item possibly loose?
         if blocks.len() == 1 {
             if let Some(Block::Paragraph(para)) = blocks.first() {
-                // yes, so store the range and wait to finish the check on
+                // yes, so store the end row and wait to finish the check on
                 // next item
-                last_para_range = Some(para.source_info.range.clone());
+                last_para_end_row = para
+                    .source_info
+                    .map_offset(para.source_info.length(), &context.source_context)
+                    .map(|mapped| mapped.location.row);
             } else {
                 // if the first block is not a paragraph, it's not loose
-                last_para_range = None;
+                last_para_end_row = None;
             }
         } else {
             // if the item has multiple blocks (but not multiple paragraphs,
             // which would have been caught above), we need to reset the
-            // last_para_range since this item can't participate in loose detection
-            last_para_range = None;
+            // last_para_end_row since this item can't participate in loose detection
+            last_para_end_row = None;
         }
-        last_item_end_row = blocks
-            .last()
-            .map(|b| get_block_source_info(b).range.end.row);
+        last_item_end_row = blocks.last().and_then(|b| {
+            let source_info = get_block_source_info(b);
+            source_info
+                .map_offset(source_info.length(), &context.source_context)
+                .map(|mapped| mapped.location.row)
+        });
         list_items.push(blocks);
     }
 
@@ -361,7 +370,7 @@ fn process_native_inline<T: Write>(
         PandocNativeIntermediate::IntermediateBaseText(text, range) => {
             if let Some(_) = whitespace_re.find(&text) {
                 Inline::Space(Space {
-                    source_info: quarto_source_map::SourceInfo::original(
+                    source_info: quarto_source_map::SourceInfo::from_range(
                         context.current_file_id(),
                         range,
                     ),
@@ -369,7 +378,7 @@ fn process_native_inline<T: Write>(
             } else {
                 Inline::Str(Str {
                     text: apply_smart_quotes(text),
-                    source_info: quarto_source_map::SourceInfo::original(
+                    source_info: quarto_source_map::SourceInfo::from_range(
                         context.current_file_id(),
                         range,
                     ),
@@ -431,7 +440,7 @@ fn process_native_inlines<T: Write>(
             PandocNativeIntermediate::IntermediateBaseText(text, range) => {
                 if let Some(_) = whitespace_re.find(&text) {
                     inlines.push(Inline::Space(Space {
-                        source_info: quarto_source_map::SourceInfo::original(
+                        source_info: quarto_source_map::SourceInfo::from_range(
                             context.current_file_id(),
                             range,
                         ),
@@ -439,7 +448,7 @@ fn process_native_inlines<T: Write>(
                 } else {
                     inlines.push(Inline::Str(Str {
                         text: apply_smart_quotes(text),
-                        source_info: quarto_source_map::SourceInfo::original(
+                        source_info: quarto_source_map::SourceInfo::from_range(
                             context.current_file_id(),
                             range,
                         ),
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/backslash_escape.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/backslash_escape.rs
index 8e0588a..ca62c23 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/backslash_escape.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/backslash_escape.rs
@@ -20,8 +20,10 @@ pub fn process_backslash_escape(
         panic!("Invalid backslash escape: {}", text);
     }
     let content = &text[1..]; // remove the leading backslash
-    PandocNativeIntermediate::IntermediateBaseText(
-        content.to_string(),
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateBaseText(content.to_string(), range)
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/block_quote.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/block_quote.rs
index c427e90..b07d13c 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/block_quote.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/block_quote.rs
@@ -46,7 +46,7 @@ pub fn process_block_quote<T: Write>(
                 content.push(Block::RawBlock(RawBlock {
                     format: "quarto_minus_metadata".to_string(),
                     text,
-                    source_info: quarto_source_map::SourceInfo::original(
+                    source_info: quarto_source_map::SourceInfo::from_range(
                         quarto_source_map::FileId(0),
                         range,
                     ),
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_fence_content.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_fence_content.rs
index 2fc106c..d5bb5f5 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_fence_content.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_fence_content.rs
@@ -44,8 +44,10 @@ pub fn process_code_fence_content(
         let slice_after_continuation = &input_bytes[current_location..end];
         content.push_str(std::str::from_utf8(slice_after_continuation).unwrap());
     }
-    PandocNativeIntermediate::IntermediateBaseText(
-        content,
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateBaseText(content, range)
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_span.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_span.rs
index 13839e0..b0c0744 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_span.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/code_span.rs
@@ -26,14 +26,18 @@ pub fn process_code_span<T: Write>(
     let mut inlines: Vec<_> = children
         .into_iter()
         .map(|(node_name, child)| {
-            let range = node_source_info_with_context(node, context);
+            let source_info = node_source_info_with_context(node, context);
+            let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+                &source_info,
+                context,
+            );
             match child {
                 PandocNativeIntermediate::IntermediateAttr(a) => {
                     attr = a;
                     // IntermediateUnknown here "consumes" the node
                     (
                         node_name,
-                        PandocNativeIntermediate::IntermediateUnknown(range.range.clone()),
+                        PandocNativeIntermediate::IntermediateUnknown(range.clone()),
                     )
                 }
                 PandocNativeIntermediate::IntermediateRawFormat(raw, _) => {
@@ -41,7 +45,7 @@ pub fn process_code_span<T: Write>(
                     // IntermediateUnknown here "consumes" the node
                     (
                         node_name,
-                        PandocNativeIntermediate::IntermediateUnknown(range.range.clone()),
+                        PandocNativeIntermediate::IntermediateUnknown(range.clone()),
                     )
                 }
                 PandocNativeIntermediate::IntermediateBaseText(text, range) => {
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/editorial_marks.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/editorial_marks.rs
index bbc75f3..dde568c 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/editorial_marks.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/editorial_marks.rs
@@ -44,12 +44,12 @@ macro_rules! process_editorial_mark {
                         PandocNativeIntermediate::IntermediateBaseText(text, range) => {
                             if let Some(_) = whitespace_re.find(&text) {
                                 content.push(Inline::Space(Space {
-                                    source_info: quarto_source_map::SourceInfo::original(context.current_file_id(), range),
+                                    source_info: quarto_source_map::SourceInfo::from_range(context.current_file_id(), range),
                                 }))
                             } else {
                                 content.push(Inline::Str(Str {
                                     text: apply_smart_quotes(text),
-                                    source_info: quarto_source_map::SourceInfo::original(context.current_file_id(), range),
+                                    source_info: quarto_source_map::SourceInfo::from_range(context.current_file_id(), range),
                                 }))
                             }
                         }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/fenced_div_block.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/fenced_div_block.rs
index a7c746c..9e86aac 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/fenced_div_block.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/fenced_div_block.rs
@@ -67,7 +67,7 @@ pub fn process_fenced_div_block<T: Write>(
                 content.push(Block::RawBlock(RawBlock {
                     format: "quarto_minus_metadata".to_string(),
                     text,
-                    source_info: quarto_source_map::SourceInfo::original(
+                    source_info: quarto_source_map::SourceInfo::from_range(
                         quarto_source_map::FileId(0),
                         range,
                     ),
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/indented_code_block.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/indented_code_block.rs
index 02de385..39416ff 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/indented_code_block.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/indented_code_block.rs
@@ -36,11 +36,9 @@ pub fn process_indented_code_block(
                     let continuation_start = range
                         .start
                         .offset
-                        .saturating_sub(outer_range.range.start.offset);
-                    let continuation_end = range
-                        .end
-                        .offset
-                        .saturating_sub(outer_range.range.start.offset);
+                        .saturating_sub(outer_range.start_offset());
+                    let continuation_end =
+                        range.end.offset.saturating_sub(outer_range.start_offset());
 
                     // Append content before this continuation
                     if continuation_start > start_offset && continuation_start <= outer_string.len()
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/link_title.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/link_title.rs
index 003470a..681cbfd 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/link_title.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/link_title.rs
@@ -15,8 +15,10 @@ pub fn process_link_title(
 ) -> PandocNativeIntermediate {
     let title = node.utf8_text(input_bytes).unwrap().to_string();
     let title = title[1..title.len() - 1].to_string();
-    PandocNativeIntermediate::IntermediateBaseText(
-        title,
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateBaseText(title, range)
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/list_marker.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/list_marker.rs
index ba6aca6..f26d239 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/list_marker.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/list_marker.rs
@@ -26,10 +26,12 @@ pub fn process_list_marker(
     if marker_text == "(@)" {
         // For example lists, we use 1 as the starting number
         // The actual numbering will be handled in postprocessing
-        return PandocNativeIntermediate::IntermediateOrderedListMarker(
-            1,
-            node_source_info_with_context(node, context).range,
+        let source_info = node_source_info_with_context(node, context);
+        let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+            &source_info,
+            context,
         );
+        return PandocNativeIntermediate::IntermediateOrderedListMarker(1, range);
     }
 
     let marker_text = marker_text
@@ -39,8 +41,10 @@ pub fn process_list_marker(
     let marker_number: usize = marker_text
         .parse()
         .unwrap_or_else(|_| panic!("Invalid list marker number: {}", marker_text));
-    PandocNativeIntermediate::IntermediateOrderedListMarker(
-        marker_number,
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateOrderedListMarker(marker_number, range)
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/numeric_character_reference.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/numeric_character_reference.rs
index a7e2de2..bf8b706 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/numeric_character_reference.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/numeric_character_reference.rs
@@ -32,8 +32,10 @@ pub fn process_numeric_character_reference(
         None => text, // If we can't parse it, return the original text
     };
 
-    PandocNativeIntermediate::IntermediateBaseText(
-        result_text,
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateBaseText(result_text, range)
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_attribute.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_attribute.rs
index 8a45ee2..68c51c3 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_attribute.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_attribute.rs
@@ -13,7 +13,11 @@ pub fn process_raw_attribute(
     children: Vec<(String, PandocNativeIntermediate)>,
     context: &ASTContext,
 ) -> PandocNativeIntermediate {
-    let range = node_source_info_with_context(node, context).range;
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
     for (_, child) in children {
         match child {
             PandocNativeIntermediate::IntermediateBaseText(raw, _) => {
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_specifier.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_specifier.rs
index c5b36d8..fd9596d 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_specifier.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/raw_specifier.rs
@@ -15,15 +15,17 @@ pub fn process_raw_specifier(
 ) -> PandocNativeIntermediate {
     // like code_content but skipping first character
     let raw = node.utf8_text(input_bytes).unwrap().to_string();
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
     if raw.chars().nth(0) == Some('<') {
         PandocNativeIntermediate::IntermediateBaseText(
             "pandoc-reader:".to_string() + &raw[1..],
-            node_source_info_with_context(node, context).range,
+            range.clone(),
         )
     } else {
-        PandocNativeIntermediate::IntermediateBaseText(
-            raw[1..].to_string(),
-            node_source_info_with_context(node, context).range,
-        )
+        PandocNativeIntermediate::IntermediateBaseText(raw[1..].to_string(), range)
     }
 }
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/shortcode.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/shortcode.rs
index 6d5dc87..81e1dfc 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/shortcode.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/shortcode.rs
@@ -22,10 +22,12 @@ pub fn process_shortcode_string_arg(
     context: &ASTContext,
 ) -> PandocNativeIntermediate {
     let id = node.utf8_text(input_bytes).unwrap().to_string();
-    PandocNativeIntermediate::IntermediateShortcodeArg(
-        ShortcodeArg::String(id),
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateShortcodeArg(ShortcodeArg::String(id), range)
 }
 
 // Helper function to process shortcode_string nodes
@@ -40,10 +42,12 @@ pub fn process_shortcode_string(
             extract_quoted_text_fn()
         )
     };
-    PandocNativeIntermediate::IntermediateShortcodeArg(
-        ShortcodeArg::String(id),
-        node_source_info_with_context(node, context).range,
-    )
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
+    PandocNativeIntermediate::IntermediateShortcodeArg(ShortcodeArg::String(id), range)
 }
 
 pub fn process_shortcode_keyword_param<T: Write>(
@@ -104,7 +108,11 @@ pub fn process_shortcode_keyword_param<T: Write>(
             }
         }
     }
-    let range = node_source_info_with_context(node, context).range;
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
     PandocNativeIntermediate::IntermediateShortcodeArg(ShortcodeArg::KeyValue(result), range)
 }
 
@@ -182,7 +190,11 @@ pub fn process_shortcode_boolean(
         "false" => ShortcodeArg::Boolean(false),
         _ => panic!("Unexpected shortcode_boolean value: {}", value),
     };
-    let range = node_source_info_with_context(node, context).range;
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
     PandocNativeIntermediate::IntermediateShortcodeArg(value, range)
 }
 
@@ -192,7 +204,11 @@ pub fn process_shortcode_number(
     context: &ASTContext,
 ) -> PandocNativeIntermediate {
     let value = node.utf8_text(input_bytes).unwrap();
-    let range = node_source_info_with_context(node, context).range;
+    let source_info = node_source_info_with_context(node, context);
+    let range = crate::pandoc::source_map_compat::source_info_to_qsm_range_or_fallback(
+        &source_info,
+        context,
+    );
     let Ok(num) = value.parse::<f64>() else {
         panic!("Invalid shortcode_number: {}", value)
     };
diff --git a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/text_helpers.rs b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/text_helpers.rs
index 94d5a4d..7bee649 100644
--- a/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/text_helpers.rs
+++ b/crates/quarto-markdown-pandoc/src/pandoc/treesitter_utils/text_helpers.rs
@@ -119,14 +119,14 @@ pub fn create_line_break_inline(
     let range = node_location(node);
     let inline = if is_hard {
         Inline::LineBreak(LineBreak {
-            source_info: quarto_source_map::SourceInfo::original(
+            source_info: quarto_source_map::SourceInfo::from_range(
                 quarto_source_map::FileId(0),
                 range,
             ),
         })
     } else {
         Inline::SoftBreak(SoftBreak {
-            source_info: quarto_source_map::SourceInfo::original(
+            source_info: quarto_source_map::SourceInfo::from_range(
                 quarto_source_map::FileId(0),
                 range,
             ),
diff --git a/crates/quarto-markdown-pandoc/src/readers/json.rs b/crates/quarto-markdown-pandoc/src/readers/json.rs
index 5300f8e..5c5032f 100644
--- a/crates/quarto-markdown-pandoc/src/readers/json.rs
+++ b/crates/quarto-markdown-pandoc/src/readers/json.rs
@@ -18,7 +18,7 @@ use crate::pandoc::{
     RawBlock, RawInline, SmallCaps, SoftBreak, Space, Span, Str, Strikeout, Strong, Subscript,
     Superscript, Underline,
 };
-use quarto_source_map::{FileId, RangeMapping, SourceMapping};
+use quarto_source_map::FileId;
 use serde_json::Value;
 use std::rc::Rc;
 
@@ -80,8 +80,11 @@ impl SourceInfoDeserializer {
 
     /// Build the pool from the sourceInfoPool JSON array (compact format)
     ///
-    /// Compact format: {"r": [start_off, start_row, start_col, end_off, end_row, end_col], "t": type_code, "d": data}
+    /// New format: {"r": [start_offset, end_offset], "t": type_code, "d": data}
+    /// Old format: {"r": [start_off, start_row, start_col, end_off, end_row, end_col], "t": type_code, "d": data}
     /// ID is implicit from array index
+    ///
+    /// Note: Row/column information from old format is ignored since SourceInfo now stores only offsets.
     fn new(pool_json: &Value) -> Result<Self> {
         let pool_array = pool_json
             .as_array()
@@ -91,45 +94,39 @@ impl SourceInfoDeserializer {
 
         // Build pool in order - parents must come before children
         for item in pool_array {
-            // Parse range from "r" array: [start_offset, start_row, start_col, end_offset, end_row, end_col]
+            // Parse offsets from "r" array
             let range_array = item
                 .get("r")
                 .and_then(|v| v.as_array())
                 .ok_or(JsonReadError::MalformedSourceInfoPool)?;
 
-            if range_array.len() != 6 {
-                return Err(JsonReadError::MalformedSourceInfoPool);
-            }
-
-            let range = quarto_source_map::Range {
-                start: quarto_source_map::Location {
-                    offset: range_array[0]
-                        .as_u64()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                    row: range_array[1]
-                        .as_u64()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                    column: range_array[2]
+            let (start_offset, end_offset) = match range_array.len() {
+                2 => {
+                    // New format: [start_offset, end_offset]
+                    let start = range_array[0]
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                },
-                end: quarto_source_map::Location {
-                    offset: range_array[3]
+                        as usize;
+                    let end = range_array[1]
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                    row: range_array[4]
+                        as usize;
+                    (start, end)
+                }
+                6 => {
+                    // Old format: [start_offset, start_row, start_col, end_offset, end_row, end_col]
+                    // Extract only offsets, ignore row/column
+                    let start = range_array[0]
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                    column: range_array[5]
+                        as usize;
+                    let end = range_array[3]
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize,
-                },
+                        as usize;
+                    (start, end)
+                }
+                _ => return Err(JsonReadError::MalformedSourceInfoPool),
             };
 
             // Parse type code from "t"
@@ -143,42 +140,47 @@ impl SourceInfoDeserializer {
                 .get("d")
                 .ok_or(JsonReadError::MalformedSourceInfoPool)?;
 
-            let mapping = match type_code {
+            let source_info = match type_code {
                 0 => {
                     // Original: data is file_id (number)
                     let file_id = data
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
                         as usize;
-                    SourceMapping::Original {
+                    quarto_source_map::SourceInfo::Original {
                         file_id: FileId(file_id),
+                        start_offset,
+                        end_offset,
                     }
                 }
                 1 => {
-                    // Substring: data is [parent_id, offset]
-                    let data_array = data
-                        .as_array()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?;
-                    if data_array.len() != 2 {
+                    // Substring: data is parent_id (new format) or [parent_id, offset] (old format)
+                    // In new format, offsets are already in start_offset/end_offset above
+                    let parent_id = if let Some(id) = data.as_u64() {
+                        // New format: just parent_id
+                        id as usize
+                    } else if let Some(data_array) = data.as_array() {
+                        // Old format: [parent_id, offset] - ignore offset, use start_offset/end_offset
+                        if data_array.len() != 2 {
+                            return Err(JsonReadError::MalformedSourceInfoPool);
+                        }
+                        data_array[0]
+                            .as_u64()
+                            .ok_or(JsonReadError::MalformedSourceInfoPool)?
+                            as usize
+                    } else {
                         return Err(JsonReadError::MalformedSourceInfoPool);
-                    }
-                    let parent_id = data_array[0]
-                        .as_u64()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize;
-                    let offset = data_array[1]
-                        .as_u64()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                        as usize;
+                    };
 
                     let parent = pool
                         .get(parent_id)
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
                         .clone();
 
-                    SourceMapping::Substring {
+                    quarto_source_map::SourceInfo::Substring {
                         parent: Rc::new(parent),
-                        offset,
+                        start_offset,
+                        end_offset,
                     }
                 }
                 2 => {
@@ -222,62 +224,33 @@ impl SourceInfoDeserializer {
                         })
                         .collect();
 
-                    SourceMapping::Concat { pieces: pieces? }
+                    quarto_source_map::SourceInfo::Concat { pieces: pieces? }
                 }
                 3 => {
-                    // Transformed: data is [parent_id, [[from_start, from_end, to_start, to_end], ...]]
+                    // Transformed variant no longer exists in SourceInfo
+                    // Convert to approximate Substring pointing to parent
+                    // This loses the transformation mapping but preserves the parent relationship
                     let data_array = data
                         .as_array()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?;
-                    if data_array.len() != 2 {
+                    if data_array.is_empty() {
                         return Err(JsonReadError::MalformedSourceInfoPool);
                     }
                     let parent_id = data_array[0]
                         .as_u64()
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
                         as usize;
-                    let mapping_array = data_array[1]
-                        .as_array()
-                        .ok_or(JsonReadError::MalformedSourceInfoPool)?;
-
-                    let range_mappings: Result<Vec<RangeMapping>> = mapping_array
-                        .iter()
-                        .map(|rm_array| {
-                            let rm = rm_array
-                                .as_array()
-                                .ok_or(JsonReadError::MalformedSourceInfoPool)?;
-                            if rm.len() != 4 {
-                                return Err(JsonReadError::MalformedSourceInfoPool);
-                            }
-                            Ok(RangeMapping {
-                                from_start: rm[0]
-                                    .as_u64()
-                                    .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                                    as usize,
-                                from_end: rm[1]
-                                    .as_u64()
-                                    .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                                    as usize,
-                                to_start: rm[2]
-                                    .as_u64()
-                                    .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                                    as usize,
-                                to_end: rm[3]
-                                    .as_u64()
-                                    .ok_or(JsonReadError::MalformedSourceInfoPool)?
-                                    as usize,
-                            })
-                        })
-                        .collect();
 
                     let parent = pool
                         .get(parent_id)
                         .ok_or(JsonReadError::MalformedSourceInfoPool)?
                         .clone();
 
-                    SourceMapping::Transformed {
+                    // Approximate with Substring
+                    quarto_source_map::SourceInfo::Substring {
                         parent: Rc::new(parent),
-                        mapping: range_mappings?,
+                        start_offset,
+                        end_offset,
                     }
                 }
                 _ => {
@@ -285,7 +258,7 @@ impl SourceInfoDeserializer {
                 }
             };
 
-            pool.push(quarto_source_map::SourceInfo { range, mapping });
+            pool.push(source_info);
         }
 
         Ok(SourceInfoDeserializer { pool })
@@ -320,7 +293,7 @@ fn make_source_info(filename_index: Option<usize>, range: Range) -> quarto_sourc
             column: range.end.column,
         },
     };
-    quarto_source_map::SourceInfo::original(file_id, qsm_range)
+    quarto_source_map::SourceInfo::from_range(file_id, qsm_range)
 }
 
 fn empty_range() -> Range {
@@ -448,6 +421,19 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
         .and_then(|v| v.as_str())
         .ok_or_else(|| JsonReadError::MissingField("t".to_string()))?;
 
+    // Extract source information - try new format ("s" field) first, fall back to old format ("l" field)
+    let source_info = if let Some(s_val) = obj.get("s") {
+        // New format: source info reference to pool
+        deserializer.from_json_ref(s_val)?
+    } else {
+        // Old format: inline location
+        let (filename_index, range) = obj
+            .get("l")
+            .and_then(read_location)
+            .unwrap_or_else(|| (None, empty_range()));
+        make_source_info(filename_index, range)
+    };
+
     match t {
         "Str" => {
             let c = obj
@@ -459,38 +445,13 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
                     JsonReadError::InvalidType("Str content must be string".to_string())
                 })?
                 .to_string();
-            Ok(Inline::Str(Str {
-                text,
-                source_info: make_source_info(None, empty_range()),
-            }))
-        }
-        "Space" => {
-            let (filename_index, range) = obj
-                .get("l")
-                .and_then(read_location)
-                .unwrap_or_else(|| (None, empty_range()));
-            Ok(Inline::Space(Space {
-                source_info: make_source_info(filename_index, range),
-            }))
-        }
-        "LineBreak" => {
-            let (filename_index, range) = obj
-                .get("l")
-                .and_then(read_location)
-                .unwrap_or_else(|| (None, empty_range()));
-            Ok(Inline::LineBreak(crate::pandoc::inline::LineBreak {
-                source_info: make_source_info(filename_index, range),
-            }))
-        }
-        "SoftBreak" => {
-            let (filename_index, range) = obj
-                .get("l")
-                .and_then(read_location)
-                .unwrap_or_else(|| (None, empty_range()));
-            Ok(Inline::SoftBreak(SoftBreak {
-                source_info: make_source_info(filename_index, range),
-            }))
+            Ok(Inline::Str(Str { text, source_info }))
         }
+        "Space" => Ok(Inline::Space(Space { source_info })),
+        "LineBreak" => Ok(Inline::LineBreak(crate::pandoc::inline::LineBreak {
+            source_info,
+        })),
+        "SoftBreak" => Ok(Inline::SoftBreak(SoftBreak { source_info })),
         "Emph" => {
             let c = obj
                 .get("c")
@@ -498,7 +459,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Emph(Emph {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Strong" => {
@@ -508,7 +469,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Strong(Strong {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Code" => {
@@ -531,7 +492,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::Code(Code {
                 attr,
                 text,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Math" => {
@@ -572,7 +533,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::Math(Math {
                 math_type,
                 text,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Underline" => {
@@ -582,7 +543,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Underline(Underline {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Strikeout" => {
@@ -592,7 +553,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Strikeout(Strikeout {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Superscript" => {
@@ -602,7 +563,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Superscript(Superscript {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Subscript" => {
@@ -612,7 +573,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::Subscript(Subscript {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "SmallCaps" => {
@@ -622,7 +583,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_inlines(c, deserializer)?;
             Ok(Inline::SmallCaps(SmallCaps {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Quoted" => {
@@ -660,7 +621,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::Quoted(Quoted {
                 quote_type,
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Link" => {
@@ -701,7 +662,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
                 attr,
                 content,
                 target,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "RawInline" => {
@@ -731,7 +692,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::RawInline(RawInline {
                 format,
                 text,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Image" => {
@@ -774,7 +735,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
                 attr,
                 content,
                 target,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Span" => {
@@ -795,7 +756,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::Span(Span {
                 attr,
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Note" => {
@@ -805,7 +766,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             let content = read_blocks(c, deserializer)?;
             Ok(Inline::Note(Note {
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         "Cite" => {
@@ -887,7 +848,7 @@ fn read_inline(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<I
             Ok(Inline::Cite(Cite {
                 citations,
                 content,
-                source_info: make_source_info(None, empty_range()),
+                source_info,
             }))
         }
         _ => Err(JsonReadError::UnsupportedVariant(format!("Inline: {}", t))),
@@ -906,27 +867,63 @@ fn read_ast_context(value: &Value) -> Result<ASTContext> {
         .as_object()
         .ok_or_else(|| JsonReadError::InvalidType("Expected object for ASTContext".to_string()))?;
 
-    let filenames_val = obj
-        .get("filenames")
-        .ok_or_else(|| JsonReadError::MissingField("filenames".to_string()))?;
+    // Read files array - each entry has "name" and optionally "line_breaks"/"total_length"
+    let files_val = obj
+        .get("files")
+        .ok_or_else(|| JsonReadError::MissingField("files".to_string()))?;
 
-    let filenames_arr = filenames_val
+    let files_arr = files_val
         .as_array()
-        .ok_or_else(|| JsonReadError::InvalidType("filenames must be array".to_string()))?;
+        .ok_or_else(|| JsonReadError::InvalidType("files must be array".to_string()))?;
+
+    let mut filenames = Vec::new();
+    let mut source_context = quarto_source_map::SourceContext::new();
+
+    for file_obj in files_arr {
+        let file_map = file_obj
+            .as_object()
+            .ok_or_else(|| JsonReadError::InvalidType("file entry must be object".to_string()))?;
+
+        // Extract filename
+        let filename = file_map
+            .get("name")
+            .and_then(|v| v.as_str())
+            .ok_or_else(|| JsonReadError::MissingField("name in file entry".to_string()))?
+            .to_string();
+
+        filenames.push(filename.clone());
+
+        // Try to extract FileInformation fields
+        let has_line_breaks = file_map.get("line_breaks").is_some();
+        let has_total_length = file_map.get("total_length").is_some();
+
+        if has_line_breaks && has_total_length {
+            // Deserialize FileInformation from the fields
+            let line_breaks: Vec<usize> = serde_json::from_value(
+                file_map.get("line_breaks").unwrap().clone(),
+            )
+            .map_err(|_| {
+                JsonReadError::InvalidType("line_breaks must be array of numbers".to_string())
+            })?;
 
-    let filenames = filenames_arr
-        .iter()
-        .map(|v| {
-            v.as_str()
-                .ok_or_else(|| JsonReadError::InvalidType("filename must be string".to_string()))
-                .map(|s| s.to_string())
-        })
-        .collect::<Result<Vec<_>>>()?;
+            let total_length: usize = serde_json::from_value(
+                file_map.get("total_length").unwrap().clone(),
+            )
+            .map_err(|_| JsonReadError::InvalidType("total_length must be number".to_string()))?;
+
+            let file_info =
+                quarto_source_map::FileInformation::from_parts(line_breaks, total_length);
+            source_context.add_file_with_info(filename, file_info);
+        } else {
+            // No FileInformation - try to read from disk
+            source_context.add_file(filename, None);
+        }
+    }
 
     Ok(ASTContext {
         filenames,
         example_list_counter: std::cell::Cell::new(1),
-        source_context: quarto_source_map::SourceContext::new(),
+        source_context,
     })
 }
 
@@ -1314,11 +1311,18 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
         .and_then(|v| v.as_str())
         .ok_or_else(|| JsonReadError::MissingField("t".to_string()))?;
 
-    // Extract location information if present
-    let (filename_index, range) = obj
-        .get("l")
-        .and_then(read_location)
-        .unwrap_or_else(|| (None, empty_range()));
+    // Extract source information - try new format ("s" field) first, fall back to old format ("l" field)
+    let source_info = if let Some(s_val) = obj.get("s") {
+        // New format: source info reference to pool
+        deserializer.from_json_ref(s_val)?
+    } else {
+        // Old format: inline location
+        let (filename_index, range) = obj
+            .get("l")
+            .and_then(read_location)
+            .unwrap_or_else(|| (None, empty_range()));
+        make_source_info(filename_index, range)
+    };
 
     match t {
         "Para" => {
@@ -1328,7 +1332,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             let content = read_inlines(c, deserializer)?;
             Ok(Block::Paragraph(Paragraph {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "Plain" => {
@@ -1338,7 +1342,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             let content = read_inlines(c, deserializer)?;
             Ok(Block::Plain(Plain {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "LineBlock" => {
@@ -1354,7 +1358,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 .collect::<Result<Vec<_>>>()?;
             Ok(Block::LineBlock(LineBlock {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "CodeBlock" => {
@@ -1379,7 +1383,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             Ok(Block::CodeBlock(CodeBlock {
                 attr,
                 text,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "RawBlock" => {
@@ -1409,7 +1413,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             Ok(Block::RawBlock(RawBlock {
                 format,
                 text,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "BlockQuote" => {
@@ -1419,7 +1423,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             let content = read_blocks(c, deserializer)?;
             Ok(Block::BlockQuote(BlockQuote {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "OrderedList" => {
@@ -1439,7 +1443,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             Ok(Block::OrderedList(OrderedList {
                 attr,
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "BulletList" => {
@@ -1449,7 +1453,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             let content = read_blockss(c, deserializer)?;
             Ok(Block::BulletList(BulletList {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "DefinitionList" => {
@@ -1477,7 +1481,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 .collect::<Result<Vec<_>>>()?;
             Ok(Block::DefinitionList(DefinitionList {
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "Header" => {
@@ -1501,12 +1505,10 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 level,
                 attr,
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
-        "HorizontalRule" => Ok(Block::HorizontalRule(HorizontalRule {
-            source_info: make_source_info(filename_index, range),
-        })),
+        "HorizontalRule" => Ok(Block::HorizontalRule(HorizontalRule { source_info })),
         "Figure" => {
             let c = obj
                 .get("c")
@@ -1526,7 +1528,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 attr,
                 caption,
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "Table" => {
@@ -1566,7 +1568,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 head,
                 bodies,
                 foot,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "Div" => {
@@ -1586,7 +1588,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
             Ok(Block::Div(Div {
                 attr,
                 content,
-                source_info: make_source_info(filename_index, range),
+                source_info,
             }))
         }
         "BlockMetadata" => {
@@ -1595,10 +1597,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 .ok_or_else(|| JsonReadError::MissingField("c".to_string()))?;
             // BlockMetadata uses MetaValueWithSourceInfo format (not top-level meta)
             let meta = read_meta_value_with_source_info(c, deserializer)?;
-            Ok(Block::BlockMetadata(MetaBlock {
-                meta,
-                source_info: make_source_info(filename_index, range),
-            }))
+            Ok(Block::BlockMetadata(MetaBlock { meta, source_info }))
         }
         "NoteDefinitionPara" => {
             let c = obj
@@ -1623,7 +1622,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 crate::pandoc::block::NoteDefinitionPara {
                     id,
                     content,
-                    source_info: make_source_info(filename_index, range),
+                    source_info,
                 },
             ))
         }
@@ -1654,7 +1653,7 @@ fn read_block(value: &Value, deserializer: &SourceInfoDeserializer) -> Result<Bl
                 crate::pandoc::block::NoteDefinitionFencedBlock {
                     id,
                     content,
-                    source_info: make_source_info(filename_index, range),
+                    source_info,
                 },
             ))
         }
diff --git a/crates/quarto-markdown-pandoc/src/readers/qmd_error_messages.rs b/crates/quarto-markdown-pandoc/src/readers/qmd_error_messages.rs
index 0f3cb6b..5e6032f 100644
--- a/crates/quarto-markdown-pandoc/src/readers/qmd_error_messages.rs
+++ b/crates/quarto-markdown-pandoc/src/readers/qmd_error_messages.rs
@@ -403,7 +403,7 @@ fn error_diagnostic_from_parse_state(
         start: start_location,
         end: end_location,
     };
-    let source_info = quarto_source_map::SourceInfo::original(
+    let source_info = quarto_source_map::SourceInfo::from_range(
         quarto_source_map::FileId(0), // File ID 0 (set up in ASTContext)
         range,
     );
@@ -432,12 +432,36 @@ fn error_diagnostic_from_parse_state(
                                 calculate_byte_offset(&input_str, token.row, token.column);
                             let token_span_end = token_byte_offset + token.size.max(1);
 
-                            // Use SourceInfo::substring to create a SourceInfo for this token
-                            // This properly uses the quarto-source-map infrastructure
-                            let token_source_info = quarto_source_map::SourceInfo::substring(
-                                source_info.clone(),
-                                token_byte_offset,
+                            // Create SourceInfo for this token location
+                            // Use from_range to create an Original SourceInfo since the token
+                            // is in the same file as the main error, not a substring of it
+                            let token_location_start =
+                                quarto_source_map::utils::offset_to_location(
+                                    &input_str,
+                                    token_byte_offset,
+                                )
+                                .unwrap_or(
+                                    quarto_source_map::Location {
+                                        offset: token_byte_offset,
+                                        row: token.row,
+                                        column: token.column,
+                                    },
+                                );
+                            let token_location_end = quarto_source_map::utils::offset_to_location(
+                                &input_str,
                                 token_span_end,
+                            )
+                            .unwrap_or(quarto_source_map::Location {
+                                offset: token_span_end,
+                                row: token.row,
+                                column: token.column + token.size.max(1),
+                            });
+                            let token_source_info = quarto_source_map::SourceInfo::from_range(
+                                quarto_source_map::FileId(0),
+                                quarto_source_map::Range {
+                                    start: token_location_start,
+                                    end: token_location_end,
+                                },
                             );
 
                             // Add as info detail with location (will show as blue label in Ariadne)
@@ -467,12 +491,36 @@ fn error_diagnostic_from_parse_state(
                                 calculate_byte_offset(&input_str, end_tok.row, end_tok.column);
                             let range_span_end = end_byte_offset + end_tok.size.max(1);
 
-                            // Use SourceInfo::substring to create a SourceInfo for this range
-                            // This properly uses the quarto-source-map infrastructure
-                            let range_source_info = quarto_source_map::SourceInfo::substring(
-                                source_info.clone(),
-                                begin_byte_offset,
+                            // Create SourceInfo for this range location
+                            // Use from_range to create an Original SourceInfo since the range
+                            // is in the same file as the main error, not a substring of it
+                            let range_location_start =
+                                quarto_source_map::utils::offset_to_location(
+                                    &input_str,
+                                    begin_byte_offset,
+                                )
+                                .unwrap_or(
+                                    quarto_source_map::Location {
+                                        offset: begin_byte_offset,
+                                        row: begin_tok.row,
+                                        column: begin_tok.column,
+                                    },
+                                );
+                            let range_location_end = quarto_source_map::utils::offset_to_location(
+                                &input_str,
                                 range_span_end,
+                            )
+                            .unwrap_or(quarto_source_map::Location {
+                                offset: range_span_end,
+                                row: end_tok.row,
+                                column: end_tok.column + end_tok.size.max(1),
+                            });
+                            let range_source_info = quarto_source_map::SourceInfo::from_range(
+                                quarto_source_map::FileId(0),
+                                quarto_source_map::Range {
+                                    start: range_location_start,
+                                    end: range_location_end,
+                                },
                             );
 
                             // Add as info detail with location
@@ -497,7 +545,6 @@ fn error_diagnostic_from_parse_state(
 fn calculate_byte_offset(input: &str, row: usize, column: usize) -> usize {
     let mut current_row = 0;
     let mut current_col = 0;
-    let mut byte_offset = 0;
 
     for (i, ch) in input.char_indices() {
         if current_row == row && current_col == column {
@@ -505,16 +552,25 @@ fn calculate_byte_offset(input: &str, row: usize, column: usize) -> usize {
         }
 
         if ch == '\n' {
+            current_col += 1;
+            // Check if the target is at the newline position (end of line)
+            if current_row == row && current_col == column {
+                return i;
+            }
             current_row += 1;
             current_col = 0;
         } else {
             current_col += 1;
         }
-        byte_offset = i;
     }
 
-    // Return the position even if we're past the end
-    byte_offset + 1
+    // If we're looking for EOF position, return the length
+    if current_row == row && current_col == column {
+        return input.len();
+    }
+
+    // If we couldn't find the position, clamp to EOF
+    input.len()
 }
 
 // Helper function to produce JSON-formatted error messages for use as a closure
diff --git a/crates/quarto-markdown-pandoc/src/writers/json.rs b/crates/quarto-markdown-pandoc/src/writers/json.rs
index 429d57f..d0ebba6 100644
--- a/crates/quarto-markdown-pandoc/src/writers/json.rs
+++ b/crates/quarto-markdown-pandoc/src/writers/json.rs
@@ -6,7 +6,7 @@
 use crate::pandoc::{
     ASTContext, Attr, Block, Caption, CitationMode, Inline, Inlines, ListAttributes, Pandoc,
 };
-use quarto_source_map::{FileId, Range, RangeMapping, SourceInfo, SourceMapping};
+use quarto_source_map::{FileId, SourceInfo};
 use serde::Serialize;
 use serde_json::{Value, json};
 use std::collections::HashMap;
@@ -17,11 +17,15 @@ use std::collections::HashMap;
 /// Each unique SourceInfo is assigned an ID and stored in a pool. References to parent
 /// SourceInfo objects are replaced with parent_id integers.
 ///
-/// Serializes in compact format: {"r": [6 range values], "t": type_code, "d": type_data}
+/// Serializes in compact format: {"r": [2 offset values], "t": type_code, "d": type_data}
 /// The ID is implicit from the array index in the pool.
+///
+/// Note: Row/column information is not stored in the serialized format.
+/// To get row/column, the reader must map offsets through the SourceContext.
 struct SerializableSourceInfo {
     id: usize,
-    range: Range,
+    start_offset: usize,
+    end_offset: usize,
     mapping: SerializableSourceMapping,
 }
 
@@ -33,16 +37,9 @@ impl Serialize for SerializableSourceInfo {
         use serde::ser::SerializeMap;
         let mut map = serializer.serialize_map(Some(3))?;
 
-        // Serialize range as array [start_offset, start_row, start_col, end_offset, end_row, end_col]
-        let range_array = [
-            self.range.start.offset,
-            self.range.start.row,
-            self.range.start.column,
-            self.range.end.offset,
-            self.range.end.row,
-            self.range.end.column,
-        ];
-        map.serialize_entry("r", &range_array)?;
+        // Serialize offsets as array [start_offset, end_offset]
+        let offset_array = [self.start_offset, self.end_offset];
+        map.serialize_entry("r", &offset_array)?;
 
         // Serialize type code and data based on mapping variant
         match &self.mapping {
@@ -50,9 +47,9 @@ impl Serialize for SerializableSourceInfo {
                 map.serialize_entry("t", &0)?;
                 map.serialize_entry("d", &file_id.0)?;
             }
-            SerializableSourceMapping::Substring { parent_id, offset } => {
+            SerializableSourceMapping::Substring { parent_id } => {
                 map.serialize_entry("t", &1)?;
-                map.serialize_entry("d", &[parent_id, offset])?;
+                map.serialize_entry("d", parent_id)?;
             }
             SerializableSourceMapping::Concat { pieces } => {
                 map.serialize_entry("t", &2)?;
@@ -62,14 +59,6 @@ impl Serialize for SerializableSourceInfo {
                     .collect();
                 map.serialize_entry("d", &piece_arrays)?;
             }
-            SerializableSourceMapping::Transformed { parent_id, mapping } => {
-                map.serialize_entry("t", &3)?;
-                let mapping_arrays: Vec<[usize; 4]> = mapping
-                    .iter()
-                    .map(|m| [m.from_start, m.from_end, m.to_start, m.to_end])
-                    .collect();
-                map.serialize_entry("d", &[json!(*parent_id), json!(mapping_arrays)])?;
-            }
         }
 
         map.end()
@@ -83,15 +72,10 @@ enum SerializableSourceMapping {
     },
     Substring {
         parent_id: usize,
-        offset: usize,
     },
     Concat {
         pieces: Vec<SerializableSourcePiece>,
     },
-    Transformed {
-        parent_id: usize,
-        mapping: Vec<RangeMapping>,
-    },
 }
 
 /// Serializable version of SourcePiece that uses source_info_id instead of SourceInfo.
@@ -137,26 +121,30 @@ impl SourceInfoSerializer {
             return id;
         }
 
-        // Recursively intern parents and build the serializable mapping
-        let mapping = match &source_info.mapping {
-            SourceMapping::Original { file_id } => {
-                SerializableSourceMapping::Original { file_id: *file_id }
-            }
-            SourceMapping::Substring { parent, offset } => {
-                let parent_id = self.intern(parent);
-                SerializableSourceMapping::Substring {
-                    parent_id,
-                    offset: *offset,
-                }
-            }
-            SourceMapping::Transformed { parent, mapping } => {
+        // Extract offsets and recursively intern parents to build the serializable mapping
+        let (start_offset, end_offset, mapping) = match source_info {
+            SourceInfo::Original {
+                file_id,
+                start_offset,
+                end_offset,
+            } => (
+                *start_offset,
+                *end_offset,
+                SerializableSourceMapping::Original { file_id: *file_id },
+            ),
+            SourceInfo::Substring {
+                parent,
+                start_offset,
+                end_offset,
+            } => {
                 let parent_id = self.intern(parent);
-                SerializableSourceMapping::Transformed {
-                    parent_id,
-                    mapping: mapping.clone(),
-                }
+                (
+                    *start_offset,
+                    *end_offset,
+                    SerializableSourceMapping::Substring { parent_id },
+                )
             }
-            SourceMapping::Concat { pieces } => {
+            SourceInfo::Concat { pieces } => {
                 let serializable_pieces = pieces
                     .iter()
                     .map(|piece| SerializableSourcePiece {
@@ -165,9 +153,13 @@ impl SourceInfoSerializer {
                         length: piece.length,
                     })
                     .collect();
-                SerializableSourceMapping::Concat {
-                    pieces: serializable_pieces,
-                }
+                (
+                    0,
+                    pieces.iter().map(|p| p.length).sum(),
+                    SerializableSourceMapping::Concat {
+                        pieces: serializable_pieces,
+                    },
+                )
             }
         };
 
@@ -177,7 +169,8 @@ impl SourceInfoSerializer {
         // Add to pool
         self.pool.push(SerializableSourceInfo {
             id,
-            range: source_info.range.clone(),
+            start_offset,
+            end_offset,
             mapping,
         });
 
@@ -194,24 +187,30 @@ impl SourceInfoSerializer {
     }
 }
 
-fn write_location(source_info: &quarto_source_map::SourceInfo) -> Value {
-    // Extract filename index by walking to the Original mapping
-    let filename_index = crate::pandoc::location::extract_filename_index(source_info);
-
-    json!({
-        "start": {
-            "offset": source_info.range.start.offset,
-            "row": source_info.range.start.row,
-            "column": source_info.range.start.column,
-        },
-        "end": {
-            "offset": source_info.range.end.offset,
-            "row": source_info.range.end.row,
-            "column": source_info.range.end.column,
-        },
-        "filenameIndex": filename_index,
-    })
-}
+// NOTE: This function is currently unused and would need a SourceContext parameter
+// to map offsets to row/column positions. Commenting out for now.
+// fn write_location(source_info: &quarto_source_map::SourceInfo, ctx: &SourceContext) -> Value {
+//     // Extract filename index by walking to the Original mapping
+//     let filename_index = crate::pandoc::location::extract_filename_index(source_info);
+//
+//     // Map start and end offsets to locations with row/column
+//     let start_mapped = source_info.map_offset(0, ctx).unwrap();
+//     let end_mapped = source_info.map_offset(source_info.length(), ctx).unwrap();
+//
+//     json!({
+//         "start": {
+//             "offset": source_info.start_offset(),
+//             "row": start_mapped.location.row,
+//             "column": start_mapped.location.column,
+//         },
+//         "end": {
+//             "offset": source_info.end_offset(),
+//             "row": end_mapped.location.row,
+//             "column": end_mapped.location.column,
+//         },
+//         "filenameIndex": filename_index,
+//     })
+// }
 
 fn write_attr(attr: &Attr) -> Value {
     json!([
@@ -730,7 +729,34 @@ fn write_pandoc(pandoc: &Pandoc, context: &ASTContext) -> Value {
 
     // Build astContext with pool and metaTopLevelKeySources
     let mut ast_context_obj = serde_json::Map::new();
-    ast_context_obj.insert("filenames".to_string(), json!(context.filenames));
+
+    // Serialize files array combining filenames and FileInformation
+    // Each file entry has: "name", "line_breaks", "total_length"
+    let files_array: Vec<Value> = (0..context.filenames.len())
+        .map(|idx| {
+            let filename = &context.filenames[idx];
+            let file_info = context
+                .source_context
+                .get_file(quarto_source_map::FileId(idx))
+                .and_then(|file| file.file_info.as_ref());
+
+            if let Some(info) = file_info {
+                // File with FileInformation - serialize everything
+                json!({
+                    "name": filename,
+                    "line_breaks": info.line_breaks(),
+                    "total_length": info.total_length()
+                })
+            } else {
+                // File without FileInformation - just the name
+                json!({
+                    "name": filename
+                })
+            }
+        })
+        .collect();
+
+    ast_context_obj.insert("files".to_string(), json!(files_array));
 
     // Only include sourceInfoPool if non-empty
     if !serializer.pool.is_empty() {
diff --git a/crates/quarto-markdown-pandoc/tests/snapshots/json/001.qmd.snapshot b/crates/quarto-markdown-pandoc/tests/snapshots/json/001.qmd.snapshot
index 2fb967c..f0e9efb 100644
--- a/crates/quarto-markdown-pandoc/tests/snapshots/json/001.qmd.snapshot
+++ b/crates/quarto-markdown-pandoc/tests/snapshots/json/001.qmd.snapshot
@@ -1 +1 @@
-{"astContext":{"filenames":["tests/snapshots/json/001.qmd"],"sourceInfoPool":[{"d":0,"r":[0,0,0,4,0,4],"t":0},{"d":0,"r":[4,0,4,5,0,5],"t":0},{"d":0,"r":[5,0,5,7,0,7],"t":0},{"d":0,"r":[7,0,7,8,0,8],"t":0},{"d":0,"r":[8,0,8,9,0,9],"t":0},{"d":0,"r":[9,0,9,10,0,10],"t":0},{"d":0,"r":[12,0,12,16,0,16],"t":0},{"d":0,"r":[10,0,10,18,0,18],"t":0},{"d":0,"r":[18,0,18,19,0,19],"t":0},{"d":0,"r":[19,0,19,23,0,23],"t":0},{"d":0,"r":[23,0,23,24,0,24],"t":0},{"d":[[9,0,4],[10,4,1]],"r":[0,0,0,5,0,0],"t":2},{"d":0,"r":[0,0,0,25,1,0],"t":0}]},"blocks":[{"c":[{"c":"This","s":0,"t":"Str"},{"s":1,"t":"Space"},{"c":"is","s":2,"t":"Str"},{"s":3,"t":"Space"},{"c":"a","s":4,"t":"Str"},{"s":5,"t":"Space"},{"c":[{"c":"bold","s":6,"t":"Str"}],"s":7,"t":"Strong"},{"s":8,"t":"Space"},{"c":"test.","s":11,"t":"Str"}],"s":12,"t":"Para"}],"meta":{},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
+{"astContext":{"files":[{"line_breaks":[24],"name":"tests/snapshots/json/001.qmd","total_length":25}],"sourceInfoPool":[{"d":0,"r":[0,4],"t":0},{"d":0,"r":[4,5],"t":0},{"d":0,"r":[5,7],"t":0},{"d":0,"r":[7,8],"t":0},{"d":0,"r":[8,9],"t":0},{"d":0,"r":[9,10],"t":0},{"d":0,"r":[12,16],"t":0},{"d":0,"r":[10,18],"t":0},{"d":0,"r":[18,19],"t":0},{"d":0,"r":[19,23],"t":0},{"d":0,"r":[23,24],"t":0},{"d":[[9,0,4],[10,4,1]],"r":[0,5],"t":2},{"d":0,"r":[0,25],"t":0}]},"blocks":[{"c":[{"c":"This","s":0,"t":"Str"},{"s":1,"t":"Space"},{"c":"is","s":2,"t":"Str"},{"s":3,"t":"Space"},{"c":"a","s":4,"t":"Str"},{"s":5,"t":"Space"},{"c":[{"c":"bold","s":6,"t":"Str"}],"s":7,"t":"Strong"},{"s":8,"t":"Space"},{"c":"test.","s":11,"t":"Str"}],"s":12,"t":"Para"}],"meta":{},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
diff --git a/crates/quarto-markdown-pandoc/tests/snapshots/json/002.qmd.snapshot b/crates/quarto-markdown-pandoc/tests/snapshots/json/002.qmd.snapshot
index 80f92d9..3fd26c2 100644
--- a/crates/quarto-markdown-pandoc/tests/snapshots/json/002.qmd.snapshot
+++ b/crates/quarto-markdown-pandoc/tests/snapshots/json/002.qmd.snapshot
@@ -1 +1 @@
-{"astContext":{"filenames":["tests/snapshots/json/002.qmd"],"metaTopLevelKeySources":{"nested":14,"title":12},"sourceInfoPool":[{"d":0,"r":[0,0,0,8,0,8],"t":0},{"d":0,"r":[8,0,8,9,0,9],"t":0},{"d":[[0,0,8],[1,8,1]],"r":[0,0,0,9,0,0],"t":2},{"d":0,"r":[0,0,0,63,11,0],"t":0},{"d":[3,4],"r":[0,0,0,16,0,0],"t":1},{"d":[4,7],"r":[0,0,0,9,0,0],"t":1},{"d":0,"r":[0,0,0,4,0,4],"t":0},{"d":0,"r":[37,6,0,58,9,0],"t":0},{"d":[7,4],"r":[0,0,0,12,0,0],"t":1},{"d":[8,8],"r":[0,0,0,4,0,0],"t":1},{"d":0,"r":[26,4,0,63,11,0],"t":0},{"d":[3,4],"r":[0,0,0,16,0,0],"t":1},{"d":[11,0],"r":[0,0,0,5,0,0],"t":1},{"d":[7,4],"r":[0,0,0,12,0,0],"t":1},{"d":[13,0],"r":[0,0,0,6,0,0],"t":1}]},"blocks":[{"c":[["",["hello"],[]],[]],"s":10,"t":"Div"}],"meta":{"nested":{"c":[{"c":"meta","s":6,"t":"Str"}],"s":9,"t":"MetaInlines"},"title":{"c":[{"c":"metadata1","s":2,"t":"Str"}],"s":5,"t":"MetaInlines"}},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
+{"astContext":{"files":[{"line_breaks":[3,20,24,25,35,36,40,53,57,58,62],"name":"tests/snapshots/json/002.qmd","total_length":63}],"metaTopLevelKeySources":{"nested":14,"title":12},"sourceInfoPool":[{"d":0,"r":[0,8],"t":0},{"d":0,"r":[8,9],"t":0},{"d":[[0,0,8],[1,8,1]],"r":[0,9],"t":2},{"d":0,"r":[0,63],"t":0},{"d":3,"r":[4,20],"t":1},{"d":4,"r":[7,16],"t":1},{"d":0,"r":[0,4],"t":0},{"d":0,"r":[37,58],"t":0},{"d":7,"r":[4,16],"t":1},{"d":8,"r":[8,12],"t":1},{"d":0,"r":[26,63],"t":0},{"d":3,"r":[4,20],"t":1},{"d":11,"r":[0,5],"t":1},{"d":7,"r":[4,16],"t":1},{"d":13,"r":[0,6],"t":1}]},"blocks":[{"c":[["",["hello"],[]],[]],"s":10,"t":"Div"}],"meta":{"nested":{"c":[{"c":"meta","s":6,"t":"Str"}],"s":9,"t":"MetaInlines"},"title":{"c":[{"c":"metadata1","s":2,"t":"Str"}],"s":5,"t":"MetaInlines"}},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
diff --git a/crates/quarto-markdown-pandoc/tests/snapshots/json/003.qmd.snapshot b/crates/quarto-markdown-pandoc/tests/snapshots/json/003.qmd.snapshot
index 26dc690..60aea7b 100644
--- a/crates/quarto-markdown-pandoc/tests/snapshots/json/003.qmd.snapshot
+++ b/crates/quarto-markdown-pandoc/tests/snapshots/json/003.qmd.snapshot
@@ -1 +1 @@
-{"astContext":{"filenames":["tests/snapshots/json/003.qmd"],"metaTopLevelKeySources":{"title":22},"sourceInfoPool":[{"d":0,"r":[0,0,0,8,0,8],"t":0},{"d":0,"r":[8,0,8,9,0,9],"t":0},{"d":[[0,0,8],[1,8,1]],"r":[0,0,0,9,0,0],"t":2},{"d":0,"r":[0,0,0,79,12,0],"t":0},{"d":[3,4],"r":[0,0,0,16,0,0],"t":1},{"d":[4,7],"r":[0,0,0,9,0,0],"t":1},{"d":0,"r":[37,6,0,74,10,0],"t":0},{"d":[6,4],"r":[0,0,0,28,0,0],"t":1},{"d":[7,0],"r":[0,0,0,6,0,0],"t":1},{"d":0,"r":[0,0,0,7,0,7],"t":0},{"d":[6,4],"r":[0,0,0,28,0,0],"t":1},{"d":[10,8],"r":[0,0,0,7,0,0],"t":1},{"d":[6,4],"r":[0,0,0,28,0,0],"t":1},{"d":[12,16],"r":[0,0,0,6,0,0],"t":1},{"d":0,"r":[0,0,0,4,0,4],"t":0},{"d":[6,4],"r":[0,0,0,28,0,0],"t":1},{"d":[15,24],"r":[0,0,0,4,0,0],"t":1},{"d":[6,4],"r":[0,0,0,28,0,0],"t":1},{"d":[17,6],"r":[0,0,0,22,0,0],"t":1},{"d":0,"r":[37,6,0,74,10,0],"t":0},{"d":0,"r":[26,4,0,79,12,0],"t":0},{"d":[3,4],"r":[0,0,0,16,0,0],"t":1},{"d":[21,0],"r":[0,0,0,5,0,0],"t":1}]},"blocks":[{"c":[["",["hello"],[]],[{"c":{"c":[{"key":"_scope","key_source":8,"value":{"c":[{"c":"lexical","s":9,"t":"Str"}],"s":11,"t":"MetaInlines"}},{"key":"nested","key_source":13,"value":{"c":[{"c":"meta","s":14,"t":"Str"}],"s":16,"t":"MetaInlines"}}],"s":18,"t":"MetaMap"},"s":19,"t":"BlockMetadata"}]],"s":20,"t":"Div"}],"meta":{"title":{"c":[{"c":"metadata1","s":2,"t":"Str"}],"s":5,"t":"MetaInlines"}},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
+{"astContext":{"files":[{"line_breaks":[3,20,24,25,35,36,40,56,69,73,74,78],"name":"tests/snapshots/json/003.qmd","total_length":79}],"metaTopLevelKeySources":{"title":22},"sourceInfoPool":[{"d":0,"r":[0,8],"t":0},{"d":0,"r":[8,9],"t":0},{"d":[[0,0,8],[1,8,1]],"r":[0,9],"t":2},{"d":0,"r":[0,79],"t":0},{"d":3,"r":[4,20],"t":1},{"d":4,"r":[7,16],"t":1},{"d":0,"r":[37,74],"t":0},{"d":6,"r":[4,32],"t":1},{"d":7,"r":[0,6],"t":1},{"d":0,"r":[0,7],"t":0},{"d":6,"r":[4,32],"t":1},{"d":10,"r":[8,15],"t":1},{"d":6,"r":[4,32],"t":1},{"d":12,"r":[16,22],"t":1},{"d":0,"r":[0,4],"t":0},{"d":6,"r":[4,32],"t":1},{"d":15,"r":[24,28],"t":1},{"d":6,"r":[4,32],"t":1},{"d":17,"r":[6,28],"t":1},{"d":0,"r":[37,74],"t":0},{"d":0,"r":[26,79],"t":0},{"d":3,"r":[4,20],"t":1},{"d":21,"r":[0,5],"t":1}]},"blocks":[{"c":[["",["hello"],[]],[{"c":{"c":[{"key":"_scope","key_source":8,"value":{"c":[{"c":"lexical","s":9,"t":"Str"}],"s":11,"t":"MetaInlines"}},{"key":"nested","key_source":13,"value":{"c":[{"c":"meta","s":14,"t":"Str"}],"s":16,"t":"MetaInlines"}}],"s":18,"t":"MetaMap"},"s":19,"t":"BlockMetadata"}]],"s":20,"t":"Div"}],"meta":{"title":{"c":[{"c":"metadata1","s":2,"t":"Str"}],"s":5,"t":"MetaInlines"}},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
diff --git a/crates/quarto-markdown-pandoc/tests/snapshots/json/math-with-attr.qmd.snapshot b/crates/quarto-markdown-pandoc/tests/snapshots/json/math-with-attr.qmd.snapshot
index b38b9bf..a65988a 100644
--- a/crates/quarto-markdown-pandoc/tests/snapshots/json/math-with-attr.qmd.snapshot
+++ b/crates/quarto-markdown-pandoc/tests/snapshots/json/math-with-attr.qmd.snapshot
@@ -1 +1 @@
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+{"astContext":{"files":[{"line_breaks":[23,47,71,72,114],"name":"tests/snapshots/json/table-caption-attr.qmd","total_length":115}],"sourceInfoPool":[{"d":0,"r":[75,80],"t":0},{"d":0,"r":[80,81],"t":0},{"d":0,"r":[81,88],"t":0},{"d":0,"r":[88,89],"t":0},{"d":0,"r":[72,115],"t":0},{"d":0,"r":[2,8],"t":0},{"d":0,"r":[8,9],"t":0},{"d":0,"r":[9,10],"t":0},{"d":0,"r":[2,11],"t":0},{"d":0,"r":[13,19],"t":0},{"d":0,"r":[19,20],"t":0},{"d":0,"r":[20,21],"t":0},{"d":0,"r":[13,22],"t":0},{"d":0,"r":[50,54],"t":0},{"d":0,"r":[54,55],"t":0},{"d":0,"r":[55,56],"t":0},{"d":0,"r":[50,59],"t":0},{"d":0,"r":[61,65],"t":0},{"d":0,"r":[65,66],"t":0},{"d":0,"r":[66,67],"t":0},{"d":0,"r":[61,70],"t":0},{"d":0,"r":[0,72],"t":0}]},"blocks":[{"c":[["",[],[["tbl-colwidths","[30,70]"]]],[null,[{"c":[{"c":"Table","s":0,"t":"Str"},{"s":1,"t":"Space"},{"c":"caption","s":2,"t":"Str"},{"s":3,"t":"Space"}],"s":4,"t":"Plain"}]],[[{"t":"AlignDefault"},{"t":"ColWidthDefault"}],[{"t":"AlignDefault"},{"t":"ColWidthDefault"}]],[["",[],[]],[[["",[],[]],[[["",[],[]],{"t":"AlignDefault"},1,1,[{"c":[{"c":"Column","s":5,"t":"Str"},{"s":6,"t":"Space"},{"c":"1","s":7,"t":"Str"}],"s":8,"t":"Plain"}]],[["",[],[]],{"t":"AlignDefault"},1,1,[{"c":[{"c":"Column","s":9,"t":"Str"},{"s":10,"t":"Space"},{"c":"2","s":11,"t":"Str"}],"s":12,"t":"Plain"}]]]]]],[[["",[],[]],0,[],[[["",[],[]],[[["",[],[]],{"t":"AlignDefault"},1,1,[{"c":[{"c":"Data","s":13,"t":"Str"},{"s":14,"t":"Space"},{"c":"1","s":15,"t":"Str"}],"s":16,"t":"Plain"}]],[["",[],[]],{"t":"AlignDefault"},1,1,[{"c":[{"c":"Data","s":17,"t":"Str"},{"s":18,"t":"Space"},{"c":"2","s":19,"t":"Str"}],"s":20,"t":"Plain"}]]]]]]],[["",[],[]],[]]],"s":21,"t":"Table"}],"meta":{},"pandoc-api-version":[1,23,1]}
\ No newline at end of file
diff --git a/crates/quarto-markdown-pandoc/tests/test_error_corpus.rs b/crates/quarto-markdown-pandoc/tests/test_error_corpus.rs
new file mode 100644
index 0000000..9085058
--- /dev/null
+++ b/crates/quarto-markdown-pandoc/tests/test_error_corpus.rs
@@ -0,0 +1,233 @@
+/*
+ * test_error_corpus.rs
+ *
+ * Tests to verify error messages from the error corpus produce proper output
+ */
+
+use regex::Regex;
+use std::fs;
+use std::path::PathBuf;
+
+/// Test that all files in resources/error-corpus/*.qmd produce ariadne-formatted errors
+/// with file:line:column information and source code snippets.
+#[test]
+fn test_error_corpus_ariadne_output() {
+    let corpus_dir = PathBuf::from("resources/error-corpus");
+    assert!(
+        corpus_dir.exists(),
+        "Error corpus directory should exist: {}",
+        corpus_dir.display()
+    );
+
+    // Find all .qmd files in the error corpus
+    let mut qmd_files: Vec<PathBuf> = fs::read_dir(&corpus_dir)
+        .expect("Failed to read error corpus directory")
+        .filter_map(|entry| {
+            let entry = entry.ok()?;
+            let path = entry.path();
+            if path.extension().and_then(|s| s.to_str()) == Some("qmd") {
+                Some(path)
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    qmd_files.sort();
+
+    assert!(
+        !qmd_files.is_empty(),
+        "Error corpus should contain at least one .qmd file"
+    );
+
+    // Compile regex once outside the loop
+    // Pattern matches: filename.qmd:123:456 (where 123 is line, 456 is column)
+    let location_pattern = Regex::new(r"\.qmd:\d+:\d+").expect("Invalid regex pattern");
+
+    for qmd_file in &qmd_files {
+        println!("Testing error corpus file: {}", qmd_file.display());
+
+        let content = fs::read_to_string(qmd_file)
+            .unwrap_or_else(|e| panic!("Failed to read {}: {}", qmd_file.display(), e));
+
+        // Parse the file - we expect it to fail with diagnostics
+        let result = quarto_markdown_pandoc::readers::qmd::read(
+            content.as_bytes(),
+            false, // not loose mode
+            &qmd_file.to_string_lossy(),
+            &mut std::io::sink(),
+        );
+
+        match result {
+            Ok(_) => {
+                panic!(
+                    "Expected {} to produce errors, but it parsed successfully",
+                    qmd_file.display()
+                );
+            }
+            Err(diagnostics) => {
+                assert!(
+                    !diagnostics.is_empty(),
+                    "Expected diagnostics for {}",
+                    qmd_file.display()
+                );
+
+                // Create a SourceContext for rendering
+                let mut source_context = quarto_source_map::SourceContext::new();
+                source_context.add_file(qmd_file.to_string_lossy().to_string(), Some(content));
+
+                // Render each diagnostic to text
+                // Track whether at least one diagnostic has ariadne output
+                let mut has_any_ariadne = false;
+
+                for diagnostic in &diagnostics {
+                    let text_output = diagnostic.to_text(Some(&source_context));
+
+                    // Check if this diagnostic has ariadne output
+                    // Ariadne uses box drawing characters for pretty printing
+                    let has_box_chars = text_output.contains("│")
+                        || text_output.contains("─")
+                        || text_output.contains("╭")
+                        || text_output.contains("╯");
+
+                    if has_box_chars {
+                        has_any_ariadne = true;
+
+                        // If it has ariadne output, it should have file:line:column notation
+                        assert!(
+                            location_pattern.is_match(&text_output),
+                            "Ariadne output for {} should contain file:line:column notation (pattern: .qmd:NUMBER:NUMBER). Got:\n{}",
+                            qmd_file.display(),
+                            text_output
+                        );
+                    }
+                }
+
+                // At least one diagnostic should have had ariadne output
+                assert!(
+                    has_any_ariadne,
+                    "At least one diagnostic for {} should have ariadne output",
+                    qmd_file.display()
+                );
+            }
+        }
+    }
+}
+
+/// Test that all files in resources/error-corpus/*.qmd produce JSON errors
+/// with proper source location information (file_id and offsets).
+#[test]
+fn test_error_corpus_json_locations() {
+    let corpus_dir = PathBuf::from("resources/error-corpus");
+    assert!(
+        corpus_dir.exists(),
+        "Error corpus directory should exist: {}",
+        corpus_dir.display()
+    );
+
+    // Find all .qmd files in the error corpus
+    let mut qmd_files: Vec<PathBuf> = fs::read_dir(&corpus_dir)
+        .expect("Failed to read error corpus directory")
+        .filter_map(|entry| {
+            let entry = entry.ok()?;
+            let path = entry.path();
+            if path.extension().and_then(|s| s.to_str()) == Some("qmd") {
+                Some(path)
+            } else {
+                None
+            }
+        })
+        .collect();
+
+    qmd_files.sort();
+
+    assert!(
+        !qmd_files.is_empty(),
+        "Error corpus should contain at least one .qmd file"
+    );
+
+    for qmd_file in &qmd_files {
+        println!("Testing JSON error locations for: {}", qmd_file.display());
+
+        let content = fs::read_to_string(qmd_file)
+            .unwrap_or_else(|e| panic!("Failed to read {}: {}", qmd_file.display(), e));
+
+        // Parse the file - we expect it to fail with diagnostics
+        let result = quarto_markdown_pandoc::readers::qmd::read(
+            content.as_bytes(),
+            false, // not loose mode
+            &qmd_file.to_string_lossy(),
+            &mut std::io::sink(),
+        );
+
+        match result {
+            Ok(_) => {
+                panic!(
+                    "Expected {} to produce errors, but it parsed successfully",
+                    qmd_file.display()
+                );
+            }
+            Err(diagnostics) => {
+                assert!(
+                    !diagnostics.is_empty(),
+                    "Expected diagnostics for {}",
+                    qmd_file.display()
+                );
+
+                // Check each diagnostic has location information
+                for diagnostic in &diagnostics {
+                    let json_value = diagnostic.to_json();
+
+                    // Check that the main error has a location field
+                    if json_value.get("location").is_some() {
+                        let location = json_value.get("location").unwrap();
+
+                        // Should have an Original variant with file_id and offsets
+                        let original = location.get("Original");
+                        assert!(
+                            original.is_some(),
+                            "Error location for {} should have Original variant. Got:\n{}",
+                            qmd_file.display(),
+                            serde_json::to_string_pretty(&json_value).unwrap()
+                        );
+
+                        let original = original.unwrap();
+                        assert!(
+                            original.get("file_id").is_some(),
+                            "Error location for {} should have file_id. Got:\n{}",
+                            qmd_file.display(),
+                            serde_json::to_string_pretty(&json_value).unwrap()
+                        );
+                        assert!(
+                            original.get("start_offset").is_some(),
+                            "Error location for {} should have start_offset. Got:\n{}",
+                            qmd_file.display(),
+                            serde_json::to_string_pretty(&json_value).unwrap()
+                        );
+                        assert!(
+                            original.get("end_offset").is_some(),
+                            "Error location for {} should have end_offset. Got:\n{}",
+                            qmd_file.display(),
+                            serde_json::to_string_pretty(&json_value).unwrap()
+                        );
+                    }
+
+                    // Check details also have location information
+                    if let Some(details) = json_value.get("details").and_then(|d| d.as_array()) {
+                        for detail in details {
+                            if let Some(detail_loc) = detail.get("location") {
+                                let original = detail_loc.get("Original");
+                                assert!(
+                                    original.is_some(),
+                                    "Detail location for {} should have Original variant. Got:\n{}",
+                                    qmd_file.display(),
+                                    serde_json::to_string_pretty(&json_value).unwrap()
+                                );
+                            }
+                        }
+                    }
+                }
+            }
+        }
+    }
+}
diff --git a/crates/quarto-markdown-pandoc/tests/test_inline_locations.rs b/crates/quarto-markdown-pandoc/tests/test_inline_locations.rs
index 73aed64..808a2e9 100644
--- a/crates/quarto-markdown-pandoc/tests/test_inline_locations.rs
+++ b/crates/quarto-markdown-pandoc/tests/test_inline_locations.rs
@@ -10,9 +10,13 @@ use tree_sitter_qmd::MarkdownParser;
 
 /// Helper to resolve a source info reference from the pool (compact format)
 /// Returns (start_offset, start_row, start_col, end_offset, end_row, end_col, type_code)
+///
+/// Note: The new JSON format only stores offsets, not row/column. This function computes
+/// row/column from the offsets using the FileInformation.
 fn resolve_source_ref(
     source_ref: &serde_json::Value,
     pool: &[serde_json::Value],
+    file_info: &quarto_source_map::FileInformation,
 ) -> (usize, usize, usize, usize, usize, usize, usize) {
     let ref_id = source_ref
         .as_u64()
@@ -26,13 +30,48 @@ fn resolve_source_ref(
         .as_u64()
         .expect("Expected t to be a number") as usize;
 
+    // New format: r is [start_offset, end_offset]
+    let start_offset = r[0].as_u64().unwrap() as usize;
+    let end_offset = r[1].as_u64().unwrap() as usize;
+
+    // For Substring type (t=1), we need to recursively resolve the offsets
+    // through the parent chain to get the file offsets
+    let (absolute_start, absolute_end) = match t {
+        0 => {
+            // Original: offsets are already absolute in the file
+            (start_offset, end_offset)
+        }
+        1 => {
+            // Substring: need to resolve through parent
+            let parent_id = source_info["d"].as_u64().unwrap() as usize;
+            let parent = &pool[parent_id];
+            let parent_r = parent["r"].as_array().unwrap();
+            let parent_start = parent_r[0].as_u64().unwrap() as usize;
+            // Substring offsets are relative to parent
+            (parent_start + start_offset, parent_start + end_offset)
+        }
+        2 => {
+            // Concat: use the range directly (should span all pieces)
+            (start_offset, end_offset)
+        }
+        _ => panic!("Unknown source info type: {}", t),
+    };
+
+    // Compute row/column from absolute offsets using FileInformation
+    let start_loc = file_info
+        .offset_to_location(absolute_start)
+        .expect("Failed to convert start offset to location");
+    let end_loc = file_info
+        .offset_to_location(absolute_end)
+        .expect("Failed to convert end offset to location");
+
     (
-        r[0].as_u64().unwrap() as usize, // start_offset
-        r[1].as_u64().unwrap() as usize, // start_row
-        r[2].as_u64().unwrap() as usize, // start_col
-        r[3].as_u64().unwrap() as usize, // end_offset
-        r[4].as_u64().unwrap() as usize, // end_row
-        r[5].as_u64().unwrap() as usize, // end_col
+        start_loc.offset,
+        start_loc.row,
+        start_loc.column,
+        end_loc.offset,
+        end_loc.row,
+        end_loc.column,
         t,
     )
 }
@@ -69,6 +108,9 @@ fn test_inline_source_locations() {
         .as_array()
         .expect("Expected sourceInfoPool to be an array");
 
+    // Create FileInformation for computing row/column from offsets
+    let file_info = quarto_source_map::FileInformation::new(input);
+
     // Check that the source locations are correct for the inline nodes
     let blocks = json_value["blocks"].as_array().unwrap();
     let para = &blocks[0];
@@ -79,7 +121,7 @@ fn test_inline_source_locations() {
     assert_eq!(hello_str["t"], "Str");
     assert_eq!(hello_str["c"], "hello");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _type) =
-        resolve_source_ref(&hello_str["s"], pool);
+        resolve_source_ref(&hello_str["s"], pool, &file_info);
     assert_eq!(start_col, 0);
     assert_eq!(start_off, 0);
     assert_eq!(end_col, 5);
@@ -89,7 +131,7 @@ fn test_inline_source_locations() {
     let space = &inlines[1];
     assert_eq!(space["t"], "Space");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&space["s"], pool);
+        resolve_source_ref(&space["s"], pool, &file_info);
     assert_eq!(start_col, 5);
     assert_eq!(start_off, 5);
     assert_eq!(end_col, 6);
@@ -99,7 +141,7 @@ fn test_inline_source_locations() {
     let emph = &inlines[2];
     assert_eq!(emph["t"], "Emph");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&emph["s"], pool);
+        resolve_source_ref(&emph["s"], pool, &file_info);
     assert_eq!(start_col, 6);
     assert_eq!(start_off, 6);
     assert_eq!(end_col, 13);
@@ -111,7 +153,7 @@ fn test_inline_source_locations() {
     assert_eq!(world_str["t"], "Str");
     assert_eq!(world_str["c"], "world");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&world_str["s"], pool);
+        resolve_source_ref(&world_str["s"], pool, &file_info);
     assert_eq!(start_col, 7);
     assert_eq!(start_off, 7);
     assert_eq!(end_col, 12);
@@ -122,7 +164,7 @@ fn test_inline_source_locations() {
     assert_eq!(period["t"], "Str");
     assert_eq!(period["c"], ".");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&period["s"], pool);
+        resolve_source_ref(&period["s"], pool, &file_info);
     assert_eq!(start_col, 13);
     assert_eq!(start_off, 13);
     assert_eq!(end_col, 14);
@@ -163,6 +205,9 @@ fn test_merged_strings_preserve_location() {
         .as_array()
         .expect("Expected sourceInfoPool to be an array");
 
+    // Create FileInformation for computing row/column from offsets
+    let file_info = quarto_source_map::FileInformation::new(input);
+
     let blocks = json_value["blocks"].as_array().unwrap();
     let para = &blocks[0];
     let inlines = para["c"].as_array().unwrap();
@@ -176,7 +221,7 @@ fn test_merged_strings_preserve_location() {
     assert_eq!(hello["t"], "Str");
     assert_eq!(hello["c"], "hello");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&hello["s"], pool);
+        resolve_source_ref(&hello["s"], pool, &file_info);
     assert_eq!(start_col, 0);
     assert_eq!(start_off, 0);
     assert_eq!(end_col, 5);
@@ -191,7 +236,7 @@ fn test_merged_strings_preserve_location() {
     assert_eq!(world["t"], "Str");
     assert_eq!(world["c"], "world");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&world["s"], pool);
+        resolve_source_ref(&world["s"], pool, &file_info);
     assert_eq!(start_col, 6);
     assert_eq!(start_off, 6);
     assert_eq!(end_col, 11);
@@ -232,6 +277,9 @@ fn test_separate_strings_keep_separate_locations() {
         .as_array()
         .expect("Expected sourceInfoPool to be an array");
 
+    // Create FileInformation for computing row/column from offsets
+    let file_info = quarto_source_map::FileInformation::new(input);
+
     let blocks = json_value["blocks"].as_array().unwrap();
     let para = &blocks[0];
     let inlines = para["c"].as_array().unwrap();
@@ -244,7 +292,7 @@ fn test_separate_strings_keep_separate_locations() {
     assert_eq!(a_str["t"], "Str");
     assert_eq!(a_str["c"], "a");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&a_str["s"], pool);
+        resolve_source_ref(&a_str["s"], pool, &file_info);
     assert_eq!(start_col, 0);
     assert_eq!(start_off, 0);
     assert_eq!(end_col, 1);
@@ -254,7 +302,7 @@ fn test_separate_strings_keep_separate_locations() {
     let strong = &inlines[1];
     assert_eq!(strong["t"], "Strong");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&strong["s"], pool);
+        resolve_source_ref(&strong["s"], pool, &file_info);
     assert_eq!(start_col, 1);
     assert_eq!(start_off, 1);
     assert_eq!(end_col, 6);
@@ -265,7 +313,7 @@ fn test_separate_strings_keep_separate_locations() {
     assert_eq!(c_str["t"], "Str");
     assert_eq!(c_str["c"], "c");
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&c_str["s"], pool);
+        resolve_source_ref(&c_str["s"], pool, &file_info);
     assert_eq!(start_col, 6);
     assert_eq!(start_off, 6);
     assert_eq!(end_col, 7);
@@ -306,6 +354,9 @@ fn test_note_source_location() {
         .as_array()
         .expect("Expected sourceInfoPool to be an array");
 
+    // Create FileInformation for computing row/column from offsets
+    let file_info = quarto_source_map::FileInformation::new(input);
+
     let blocks = json_value["blocks"].as_array().unwrap();
     let para = &blocks[0];
     let inlines = para["c"].as_array().unwrap();
@@ -324,7 +375,7 @@ fn test_note_source_location() {
 
     // Check Note's source location spans the entire ^[note content]
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&note["s"], pool);
+        resolve_source_ref(&note["s"], pool, &file_info);
     assert_eq!(start_col, 4);
     assert_eq!(start_off, 4);
     assert_eq!(end_col, 19);
@@ -340,7 +391,7 @@ fn test_note_source_location() {
     // CRITICAL: The Paragraph wrapper should have proper source location
     // not SourceInfo::default() which would be FileId(0) with offset 0
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&note_para["s"], pool);
+        resolve_source_ref(&note_para["s"], pool, &file_info);
 
     // The paragraph wrapper should have the same source location as the Note itself
     // since it's a synthetic wrapper for the note's content
@@ -407,6 +458,9 @@ fn test_note_reference_source_location() {
         .as_array()
         .expect("Expected sourceInfoPool to be an array");
 
+    // Create FileInformation for computing row/column from offsets
+    let file_info = quarto_source_map::FileInformation::new(input);
+
     let blocks = json_value["blocks"].as_array().unwrap();
     let para = &blocks[0];
     let inlines = para["c"].as_array().unwrap();
@@ -432,7 +486,7 @@ fn test_note_reference_source_location() {
     // CRITICAL: The Span should have proper source location from the NoteReference
     // not SourceInfo::default() which would be FileId(0) with offset 0
     let (start_off, _start_row, start_col, end_off, _end_row, end_col, _t) =
-        resolve_source_ref(&span["s"], pool);
+        resolve_source_ref(&span["s"], pool, &file_info);
 
     // The [^note1] spans from column 10 to 18 (0-indexed)
     assert_eq!(start_col, 10);
diff --git a/crates/quarto-markdown-pandoc/tests/test_json_roundtrip.rs b/crates/quarto-markdown-pandoc/tests/test_json_roundtrip.rs
index 8ace709..27f815e 100644
--- a/crates/quarto-markdown-pandoc/tests/test_json_roundtrip.rs
+++ b/crates/quarto-markdown-pandoc/tests/test_json_roundtrip.rs
@@ -18,7 +18,7 @@ fn test_json_roundtrip_simple_paragraph() {
         blocks: vec![Block::Paragraph(Paragraph {
             content: vec![Inline::Str(Str {
                 text: "Hello, world!".to_string(),
-                source_info: SourceInfo::original(
+                source_info: SourceInfo::from_range(
                     FileId(0),
                     Range {
                         start: Location {
@@ -34,7 +34,7 @@ fn test_json_roundtrip_simple_paragraph() {
                     },
                 ),
             })],
-            source_info: SourceInfo::original(
+            source_info: SourceInfo::from_range(
                 FileId(0),
                 Range {
                     start: Location {
@@ -102,7 +102,7 @@ fn test_json_roundtrip_complex_document() {
                 content: vec![
                     Inline::Str(Str {
                         text: "This is ".to_string(),
-                        source_info: SourceInfo::original(
+                        source_info: SourceInfo::from_range(
                             FileId(0),
                             Range {
                                 start: Location {
@@ -121,7 +121,7 @@ fn test_json_roundtrip_complex_document() {
                     Inline::Strong(quarto_markdown_pandoc::pandoc::Strong {
                         content: vec![Inline::Str(Str {
                             text: "bold text".to_string(),
-                            source_info: SourceInfo::original(
+                            source_info: SourceInfo::from_range(
                                 FileId(0),
                                 Range {
                                     start: Location {
@@ -137,7 +137,7 @@ fn test_json_roundtrip_complex_document() {
                                 },
                             ),
                         })],
-                        source_info: SourceInfo::original(
+                        source_info: SourceInfo::from_range(
                             FileId(0),
                             Range {
                                 start: Location {
@@ -155,7 +155,7 @@ fn test_json_roundtrip_complex_document() {
                     }),
                     Inline::Str(Str {
                         text: ".".to_string(),
-                        source_info: SourceInfo::original(
+                        source_info: SourceInfo::from_range(
                             FileId(0),
                             Range {
                                 start: Location {
@@ -172,7 +172,7 @@ fn test_json_roundtrip_complex_document() {
                         ),
                     }),
                 ],
-                source_info: SourceInfo::original(
+                source_info: SourceInfo::from_range(
                     FileId(0),
                     Range {
                         start: Location {
@@ -191,7 +191,7 @@ fn test_json_roundtrip_complex_document() {
             Block::CodeBlock(quarto_markdown_pandoc::pandoc::CodeBlock {
                 attr: ("".to_string(), vec![], HashMap::new()),
                 text: "print('Hello, world!')".to_string(),
-                source_info: SourceInfo::original(
+                source_info: SourceInfo::from_range(
                     FileId(0),
                     Range {
                         start: Location {
@@ -261,7 +261,7 @@ fn test_json_write_then_read_matches_original_structure() {
             Block::Plain(quarto_markdown_pandoc::pandoc::Plain {
                 content: vec![Inline::Str(Str {
                     text: "Plain text".to_string(),
-                    source_info: SourceInfo::original(
+                    source_info: SourceInfo::from_range(
                         FileId(0),
                         Range {
                             start: Location {
@@ -277,7 +277,7 @@ fn test_json_write_then_read_matches_original_structure() {
                         },
                     ),
                 })],
-                source_info: SourceInfo::original(
+                source_info: SourceInfo::from_range(
                     FileId(0),
                     Range {
                         start: Location {
@@ -296,7 +296,7 @@ fn test_json_write_then_read_matches_original_structure() {
             Block::RawBlock(quarto_markdown_pandoc::pandoc::RawBlock {
                 format: "html".to_string(),
                 text: "<div>Raw HTML</div>".to_string(),
-                source_info: SourceInfo::original(
+                source_info: SourceInfo::from_range(
                     FileId(0),
                     Range {
                         start: Location {
@@ -348,3 +348,117 @@ fn test_json_write_then_read_matches_original_structure() {
         _ => panic!("Block type mismatch for second block"),
     }
 }
+
+/// Test that JSON roundtrip preserves source mapping capability (map_offset should work)
+#[test]
+fn test_json_roundtrip_preserves_source_mapping() {
+    let qmd_content = r#"---
+title: "Test"
+---
+
+Hello world
+"#;
+
+    // Create a temporary file for testing
+    let temp_dir = std::env::temp_dir();
+    let test_file = temp_dir.join("test_json_roundtrip_mapping.qmd");
+    std::fs::write(&test_file, qmd_content).expect("Failed to write test file");
+
+    // Step 1: Parse QMD to create initial AST with source mapping
+    let result = readers::qmd::read(
+        qmd_content.as_bytes(),
+        false,
+        &test_file.to_string_lossy(),
+        &mut std::io::sink(),
+    );
+    let (pandoc1, context1, diagnostics) = result.expect("Failed to parse QMD");
+    assert!(diagnostics.is_empty(), "Expected no parse errors");
+
+    // Step 2: Serialize to JSON
+    let mut json_buf = Vec::new();
+    json::write(&pandoc1, &context1, &mut json_buf).expect("Failed to write JSON");
+
+    // Step 3: Verify that JSON contains files array with embedded FileInformation
+    let json_value: serde_json::Value =
+        serde_json::from_slice(&json_buf).expect("Failed to parse JSON");
+    let files_in_json = json_value["astContext"]["files"].as_array();
+    assert!(
+        files_in_json.is_some(),
+        "JSON should contain files array in astContext"
+    );
+    let files_array = files_in_json.unwrap();
+    assert_eq!(files_array.len(), 1, "Should have one file");
+
+    // Verify the file entry has name, line_breaks, and total_length
+    let file_obj = &files_array[0];
+    assert!(
+        file_obj["name"].is_string(),
+        "File entry should have name field"
+    );
+    assert!(
+        file_obj["line_breaks"].is_array(),
+        "File entry should have line_breaks array"
+    );
+    assert!(
+        file_obj["total_length"].is_number(),
+        "File entry should have total_length"
+    );
+
+    // Step 4: Deserialize from JSON
+    let (pandoc2, context2) =
+        readers::json::read(&mut json_buf.as_slice()).expect("Failed to read JSON");
+
+    // Step 5: Verify that the deserialized AST has working source mapping
+    // Get the first block (should be a Para with "Hello world")
+    if let Some(first_block) = pandoc2.blocks.first() {
+        if let Block::Paragraph(para) = first_block {
+            // Verify we have a SourceInfo (just check that it has non-zero length)
+            assert!(
+                para.source_info.length() > 0,
+                "Para block should have source info with non-zero length after JSON roundtrip"
+            );
+
+            // The key test: map_offset should work on the deserialized SourceInfo
+            let mapped_start = para.source_info.map_offset(0, &context2.source_context);
+            assert!(
+                mapped_start.is_some(),
+                "map_offset should work after JSON roundtrip (start position). \
+                 This means SourceContext should have been populated with file information from disk."
+            );
+
+            let mapped_end = para
+                .source_info
+                .map_offset(para.source_info.length(), &context2.source_context);
+            assert!(
+                mapped_end.is_some(),
+                "map_offset should work after JSON roundtrip (end position)"
+            );
+
+            // Verify the mapped locations are sensible
+            let start_loc = mapped_start.unwrap();
+            // Row 4 is where "Hello world" starts (after frontmatter and blank line)
+            assert_eq!(
+                start_loc.location.row, 4,
+                "After roundtrip, paragraph should still map to correct row"
+            );
+
+            // Also test inline elements have working source mapping
+            if let Some(Inline::Str(str_inline)) = para.content.first() {
+                let inline_mapped = str_inline
+                    .source_info
+                    .map_offset(0, &context2.source_context);
+                assert!(
+                    inline_mapped.is_some(),
+                    "map_offset should work on inline elements after roundtrip"
+                );
+            }
+        } else {
+            panic!("Expected Para block, got {:?}", first_block);
+        }
+    } else {
+        panic!("Expected at least one block in the document");
+    }
+
+    // Clean up
+    std::fs::remove_file(&test_file).ok();
+}
diff --git a/crates/quarto-markdown-pandoc/tests/test_location_health.rs b/crates/quarto-markdown-pandoc/tests/test_location_health.rs
new file mode 100644
index 0000000..693ac3d
--- /dev/null
+++ b/crates/quarto-markdown-pandoc/tests/test_location_health.rs
@@ -0,0 +1,873 @@
+//! Self-health tests for location information
+//!
+//! These tests verify invariant properties that must hold for ALL well-formed
+//! parsed documents. They are designed to run on any .qmd file in the test suite
+//! without requiring specific knowledge about the file's contents.
+//!
+//! Properties tested:
+//! 1. Well-formed ranges: start <= end in all dimensions
+//! 2. Offset/row/column consistency: conversions are proper inverses
+//! 3. Bounds checking: all locations are within valid bounds
+//! 4. Nesting consistency: child ranges contained in parent ranges
+//! 5. Sequential consistency: sibling nodes don't overlap
+//! 6. SourceMapping validity: parent references exist and are valid
+
+use quarto_markdown_pandoc::pandoc::{Block, Inline, Pandoc};
+use quarto_source_map::{Range, SourceInfo};
+use std::fmt;
+
+/// Represents a violation of location health properties
+#[derive(Debug, Clone)]
+pub struct LocationHealthViolation {
+    pub category: ViolationCategory,
+    pub message: String,
+    pub location_info: Option<String>,
+}
+
+#[derive(Debug, Clone, PartialEq, Eq)]
+pub enum ViolationCategory {
+    WellFormedRange,
+    OffsetRowColConsistency,
+    BoundsCheck,
+    NestingConsistency,
+    SequentialConsistency,
+    SourceMappingValidity,
+}
+
+impl fmt::Display for LocationHealthViolation {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "[{:?}] {}", self.category, self.message)?;
+        if let Some(loc) = &self.location_info {
+            write!(f, " at {}", loc)?;
+        }
+        Ok(())
+    }
+}
+
+/// Accumulates violations found during validation
+pub struct LocationHealthValidator {
+    violations: Vec<LocationHealthViolation>,
+    source: String,
+}
+
+impl LocationHealthValidator {
+    pub fn new(source: String) -> Self {
+        Self {
+            violations: Vec::new(),
+            source,
+        }
+    }
+
+    pub fn add_violation(
+        &mut self,
+        category: ViolationCategory,
+        message: String,
+        range: Option<&Range>,
+    ) {
+        let location_info = range.map(|r| {
+            format!(
+                "offset {}:{} (row:{},col:{}) to {}:{} (row:{},col:{})",
+                r.start.offset,
+                r.start.offset,
+                r.start.row,
+                r.start.column,
+                r.end.offset,
+                r.end.offset,
+                r.end.row,
+                r.end.column
+            )
+        });
+
+        self.violations.push(LocationHealthViolation {
+            category,
+            message,
+            location_info,
+        });
+    }
+
+    pub fn violations(&self) -> &[LocationHealthViolation] {
+        &self.violations
+    }
+
+    pub fn has_violations(&self) -> bool {
+        !self.violations.is_empty()
+    }
+
+    pub fn source(&self) -> &str {
+        &self.source
+    }
+}
+
+/// Extract all SourceInfo from a Pandoc document by walking the AST
+pub fn extract_all_source_info(doc: &Pandoc) -> Vec<SourceInfo> {
+    let mut source_infos = Vec::new();
+
+    for block in &doc.blocks {
+        collect_source_info_from_block(block, &mut source_infos);
+    }
+
+    source_infos
+}
+
+/// Recursively collect SourceInfo from a Block and its children
+fn collect_source_info_from_block(block: &Block, source_infos: &mut Vec<SourceInfo>) {
+    match block {
+        Block::Plain(plain) => {
+            source_infos.push(plain.source_info.clone());
+            for inline in &plain.content {
+                collect_source_info_from_inline(inline, source_infos);
+            }
+        }
+        Block::Paragraph(para) => {
+            source_infos.push(para.source_info.clone());
+            for inline in &para.content {
+                collect_source_info_from_inline(inline, source_infos);
+            }
+        }
+        Block::LineBlock(line_block) => {
+            source_infos.push(line_block.source_info.clone());
+            for line in &line_block.content {
+                for inline in line {
+                    collect_source_info_from_inline(inline, source_infos);
+                }
+            }
+        }
+        Block::Header(header) => {
+            source_infos.push(header.source_info.clone());
+            for inline in &header.content {
+                collect_source_info_from_inline(inline, source_infos);
+            }
+        }
+        Block::CodeBlock(code_block) => {
+            source_infos.push(code_block.source_info.clone());
+        }
+        Block::RawBlock(raw_block) => {
+            source_infos.push(raw_block.source_info.clone());
+        }
+        Block::HorizontalRule(hr) => {
+            source_infos.push(hr.source_info.clone());
+        }
+        Block::BlockQuote(quote) => {
+            source_infos.push(quote.source_info.clone());
+            for child_block in &quote.content {
+                collect_source_info_from_block(child_block, source_infos);
+            }
+        }
+        Block::Div(div) => {
+            source_infos.push(div.source_info.clone());
+            for child_block in &div.content {
+                collect_source_info_from_block(child_block, source_infos);
+            }
+        }
+        Block::BulletList(bullet_list) => {
+            source_infos.push(bullet_list.source_info.clone());
+            for item in &bullet_list.content {
+                for child_block in item {
+                    collect_source_info_from_block(child_block, source_infos);
+                }
+            }
+        }
+        Block::OrderedList(ordered_list) => {
+            source_infos.push(ordered_list.source_info.clone());
+            for item in &ordered_list.content {
+                for child_block in item {
+                    collect_source_info_from_block(child_block, source_infos);
+                }
+            }
+        }
+        Block::DefinitionList(def_list) => {
+            source_infos.push(def_list.source_info.clone());
+            for (term, definitions) in &def_list.content {
+                for inline in term {
+                    collect_source_info_from_inline(inline, source_infos);
+                }
+                for definition in definitions {
+                    for child_block in definition {
+                        collect_source_info_from_block(child_block, source_infos);
+                    }
+                }
+            }
+        }
+        Block::Table(table) => {
+            source_infos.push(table.source_info.clone());
+            // Table headers
+            for row in &table.head.rows {
+                for cell in &row.cells {
+                    for child_block in &cell.content {
+                        collect_source_info_from_block(child_block, source_infos);
+                    }
+                }
+            }
+            // Table bodies
+            for body in &table.bodies {
+                // Body head rows
+                for row in &body.head {
+                    for cell in &row.cells {
+                        for child_block in &cell.content {
+                            collect_source_info_from_block(child_block, source_infos);
+                        }
+                    }
+                }
+                // Body body rows
+                for row in &body.body {
+                    for cell in &row.cells {
+                        for child_block in &cell.content {
+                            collect_source_info_from_block(child_block, source_infos);
+                        }
+                    }
+                }
+            }
+            // Table footer
+            for row in &table.foot.rows {
+                for cell in &row.cells {
+                    for child_block in &cell.content {
+                        collect_source_info_from_block(child_block, source_infos);
+                    }
+                }
+            }
+        }
+        Block::Figure(figure) => {
+            source_infos.push(figure.source_info.clone());
+            for child_block in &figure.content {
+                collect_source_info_from_block(child_block, source_infos);
+            }
+            // Caption has optional long (blocks)
+            if let Some(long_caption) = &figure.caption.long {
+                for child_block in long_caption {
+                    collect_source_info_from_block(child_block, source_infos);
+                }
+            }
+        }
+        Block::BlockMetadata(_)
+        | Block::NoteDefinitionPara(_)
+        | Block::NoteDefinitionFencedBlock(_)
+        | Block::CaptionBlock(_) => {
+            // TODO: handle these special block types if they have source info
+        }
+    }
+}
+
+/// Recursively collect SourceInfo from an Inline and its children
+fn collect_source_info_from_inline(inline: &Inline, source_infos: &mut Vec<SourceInfo>) {
+    match inline {
+        Inline::Str(str_node) => {
+            source_infos.push(str_node.source_info.clone());
+        }
+        Inline::Emph(emph) => {
+            source_infos.push(emph.source_info.clone());
+            for child in &emph.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Underline(underline) => {
+            source_infos.push(underline.source_info.clone());
+            for child in &underline.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Strong(strong) => {
+            source_infos.push(strong.source_info.clone());
+            for child in &strong.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Strikeout(strikeout) => {
+            source_infos.push(strikeout.source_info.clone());
+            for child in &strikeout.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Superscript(sup) => {
+            source_infos.push(sup.source_info.clone());
+            for child in &sup.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Subscript(sub) => {
+            source_infos.push(sub.source_info.clone());
+            for child in &sub.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::SmallCaps(small_caps) => {
+            source_infos.push(small_caps.source_info.clone());
+            for child in &small_caps.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Quoted(quoted) => {
+            source_infos.push(quoted.source_info.clone());
+            for child in &quoted.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Cite(cite) => {
+            source_infos.push(cite.source_info.clone());
+            for child in &cite.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Code(code) => {
+            source_infos.push(code.source_info.clone());
+        }
+        Inline::Space(space) => {
+            source_infos.push(space.source_info.clone());
+        }
+        Inline::SoftBreak(soft_break) => {
+            source_infos.push(soft_break.source_info.clone());
+        }
+        Inline::LineBreak(line_break) => {
+            source_infos.push(line_break.source_info.clone());
+        }
+        Inline::Math(math) => {
+            source_infos.push(math.source_info.clone());
+        }
+        Inline::RawInline(raw) => {
+            source_infos.push(raw.source_info.clone());
+        }
+        Inline::Link(link) => {
+            source_infos.push(link.source_info.clone());
+            for child in &link.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Image(image) => {
+            source_infos.push(image.source_info.clone());
+            for child in &image.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Note(note) => {
+            source_infos.push(note.source_info.clone());
+            for child_block in &note.content {
+                collect_source_info_from_block(child_block, source_infos);
+            }
+        }
+        Inline::Span(span) => {
+            source_infos.push(span.source_info.clone());
+            for child in &span.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Shortcode(_) => {
+            // TODO: handle shortcode if it has source info
+        }
+        Inline::NoteReference(note_ref) => {
+            source_infos.push(note_ref.source_info.clone());
+        }
+        Inline::Attr(_) => {
+            // Attr doesn't have source info - it's just metadata
+        }
+        Inline::Insert(insert) => {
+            source_infos.push(insert.source_info.clone());
+            for child in &insert.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Delete(delete) => {
+            source_infos.push(delete.source_info.clone());
+            for child in &delete.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::Highlight(highlight) => {
+            source_infos.push(highlight.source_info.clone());
+            for child in &highlight.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+        Inline::EditComment(comment) => {
+            source_infos.push(comment.source_info.clone());
+            for child in &comment.content {
+                collect_source_info_from_inline(child, source_infos);
+            }
+        }
+    }
+}
+
+// ============================================================================
+// PHASE 2: Core Property Validators
+// ============================================================================
+
+/// Validate that a Range is well-formed
+fn validate_well_formed_range(range: &Range, validator: &mut LocationHealthValidator) {
+    // Check: start.offset <= end.offset
+    if range.start.offset > range.end.offset {
+        validator.add_violation(
+            ViolationCategory::WellFormedRange,
+            format!(
+                "Start offset {} is greater than end offset {}",
+                range.start.offset, range.end.offset
+            ),
+            Some(range),
+        );
+    }
+
+    // Check: start.row <= end.row
+    if range.start.row > range.end.row {
+        validator.add_violation(
+            ViolationCategory::WellFormedRange,
+            format!(
+                "Start row {} is greater than end row {}",
+                range.start.row, range.end.row
+            ),
+            Some(range),
+        );
+    }
+
+    // Check: if same row, start.column <= end.column
+    if range.start.row == range.end.row && range.start.column > range.end.column {
+        validator.add_violation(
+            ViolationCategory::WellFormedRange,
+            format!(
+                "On same row {}, start column {} is greater than end column {}",
+                range.start.row, range.start.column, range.end.column
+            ),
+            Some(range),
+        );
+    }
+}
+
+/// Validate that offset and row/column are consistent for a Location
+fn validate_offset_row_col_consistency(
+    location: &quarto_source_map::Location,
+    source: &str,
+    context: &str,
+    validator: &mut LocationHealthValidator,
+) {
+    // Check: offset_to_location(offset) should give us the same row/col
+    if let Some(computed_loc) =
+        quarto_source_map::utils::offset_to_location(source, location.offset)
+    {
+        if computed_loc.row != location.row || computed_loc.column != location.column {
+            validator.add_violation(
+                ViolationCategory::OffsetRowColConsistency,
+                format!(
+                    "{}: offset_to_location({}) returned (row:{}, col:{}) but expected (row:{}, col:{})",
+                    context,
+                    location.offset,
+                    computed_loc.row,
+                    computed_loc.column,
+                    location.row,
+                    location.column
+                ),
+                None,
+            );
+        }
+    } else {
+        validator.add_violation(
+            ViolationCategory::OffsetRowColConsistency,
+            format!(
+                "{}: offset_to_location({}) returned None (offset out of bounds)",
+                context, location.offset
+            ),
+            None,
+        );
+    }
+
+    // Check: line_col_to_offset(row, col) should give us the same offset
+    if let Some(computed_offset) =
+        quarto_source_map::utils::line_col_to_offset(source, location.row, location.column)
+    {
+        if computed_offset != location.offset {
+            validator.add_violation(
+                ViolationCategory::OffsetRowColConsistency,
+                format!(
+                    "{}: line_col_to_offset(row:{}, col:{}) returned offset {} but expected {}",
+                    context, location.row, location.column, computed_offset, location.offset
+                ),
+                None,
+            );
+        }
+    } else {
+        validator.add_violation(
+            ViolationCategory::OffsetRowColConsistency,
+            format!(
+                "{}: line_col_to_offset(row:{}, col:{}) returned None (row/col out of bounds)",
+                context, location.row, location.column
+            ),
+            None,
+        );
+    }
+}
+
+/// Validate that a Location is within valid bounds for the source
+fn validate_location_bounds(
+    location: &quarto_source_map::Location,
+    source: &str,
+    context: &str,
+    validator: &mut LocationHealthValidator,
+) {
+    let source_len = source.len();
+
+    // Check: offset <= source.len()
+    if location.offset > source_len {
+        validator.add_violation(
+            ViolationCategory::BoundsCheck,
+            format!(
+                "{}: offset {} exceeds source length {}",
+                context, location.offset, source_len
+            ),
+            None,
+        );
+    }
+
+    // Count number of lines in source
+    let num_lines = source.lines().count();
+    if num_lines == 0 && location.row != 0 {
+        validator.add_violation(
+            ViolationCategory::BoundsCheck,
+            format!(
+                "{}: row {} invalid for empty file (should be 0)",
+                context, location.row
+            ),
+            None,
+        );
+    } else if location.row >= num_lines && source_len > 0 {
+        // Allow row == num_lines for EOF position after final newline
+        // But if source is non-empty and we're beyond that, it's invalid
+        if location.row > num_lines || (location.row == num_lines && !source.ends_with('\n')) {
+            validator.add_violation(
+                ViolationCategory::BoundsCheck,
+                format!(
+                    "{}: row {} exceeds number of lines {} (ends_with_newline: {})",
+                    context,
+                    location.row,
+                    num_lines,
+                    source.ends_with('\n')
+                ),
+                None,
+            );
+        }
+    }
+}
+
+/// Validate all core properties for a single SourceInfo
+fn validate_source_info_core_properties(
+    source_info: &SourceInfo,
+    source: &str,
+    context: &str,
+    validator: &mut LocationHealthValidator,
+) {
+    let start_offset = source_info.start_offset();
+    let end_offset = source_info.end_offset();
+
+    // Build a Range object for compatibility with existing validation functions
+    // We compute the Location data from offsets using the source text
+    let start_location = quarto_source_map::utils::offset_to_location(source, start_offset)
+        .unwrap_or(quarto_source_map::Location {
+            offset: start_offset,
+            row: 0,
+            column: 0,
+        });
+
+    let end_location = quarto_source_map::utils::offset_to_location(source, end_offset).unwrap_or(
+        quarto_source_map::Location {
+            offset: end_offset,
+            row: 0,
+            column: 0,
+        },
+    );
+
+    let range = Range {
+        start: start_location,
+        end: end_location,
+    };
+
+    // 1. Well-formed range
+    validate_well_formed_range(&range, validator);
+
+    // 2. Offset/row/column consistency for start
+    validate_offset_row_col_consistency(
+        &range.start,
+        source,
+        &format!("{} start", context),
+        validator,
+    );
+
+    // 3. Offset/row/column consistency for end
+    validate_offset_row_col_consistency(&range.end, source, &format!("{} end", context), validator);
+
+    // 4. Bounds checking for start
+    validate_location_bounds(
+        &range.start,
+        source,
+        &format!("{} start", context),
+        validator,
+    );
+
+    // 5. Bounds checking for end
+    validate_location_bounds(&range.end, source, &format!("{} end", context), validator);
+}
+
+/// Run all core property validations on a Pandoc document
+pub fn validate_core_properties(doc: &Pandoc, source: &str) -> Vec<LocationHealthViolation> {
+    let mut validator = LocationHealthValidator::new(source.to_string());
+    let source_infos = extract_all_source_info(doc);
+
+    for (i, source_info) in source_infos.iter().enumerate() {
+        let context = format!("SourceInfo #{}", i);
+        validate_source_info_core_properties(source_info, source, &context, &mut validator);
+    }
+
+    validator.violations().to_vec()
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use quarto_markdown_pandoc::pandoc::{ASTContext, treesitter_to_pandoc};
+    use quarto_markdown_pandoc::utils::diagnostic_collector::DiagnosticCollector;
+    use tree_sitter_qmd::MarkdownParser;
+
+    fn parse_qmd_helper(source: &str) -> Pandoc {
+        let mut parser = MarkdownParser::default();
+        let input_bytes = source.as_bytes();
+        let tree = parser
+            .parse(input_bytes, None)
+            .expect("Failed to parse input");
+
+        let context = ASTContext::anonymous();
+        let mut error_collector = DiagnosticCollector::new();
+        treesitter_to_pandoc(
+            &mut std::io::sink(),
+            &tree,
+            input_bytes,
+            &context,
+            &mut error_collector,
+        )
+        .expect("Failed to convert to Pandoc AST")
+    }
+
+    #[test]
+    fn test_extract_source_info_simple() {
+        let source = "Hello world";
+        let doc = parse_qmd_helper(source);
+
+        let source_infos = extract_all_source_info(&doc);
+
+        // Should have at least: Paragraph, Str "Hello", Space, Str "world"
+        assert!(
+            source_infos.len() >= 4,
+            "Expected at least 4 source infos, got {}",
+            source_infos.len()
+        );
+    }
+
+    #[test]
+    fn test_extract_source_info_nested() {
+        let source = "This is *emphasis with **strong** inside*";
+        let doc = parse_qmd_helper(source);
+
+        let source_infos = extract_all_source_info(&doc);
+
+        // Should have: Paragraph, multiple Str, Emph, Strong, etc.
+        assert!(
+            source_infos.len() > 5,
+            "Expected many source infos for nested structure, got {}",
+            source_infos.len()
+        );
+    }
+
+    #[test]
+    fn test_core_properties_simple() {
+        let source = "Hello world";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for simple document"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_nested() {
+        let source = "This is *emphasis with **strong** inside*";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for nested document"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_multiline() {
+        let source = "Line 1\nLine 2\nLine 3";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for multiline document"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_empty() {
+        let source = "";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for empty document"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_no_trailing_newline() {
+        let source = "Line 1\nLine 2\nLine 3";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for document without trailing newline"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_with_trailing_newline() {
+        let source = "Line 1\nLine 2\nLine 3\n";
+        let doc = parse_qmd_helper(source);
+
+        let violations = validate_core_properties(&doc, source);
+
+        if !violations.is_empty() {
+            eprintln!("Found {} violations:", violations.len());
+            for v in &violations {
+                eprintln!("  {}", v);
+            }
+        }
+
+        assert!(
+            violations.is_empty(),
+            "Expected no violations for document with trailing newline"
+        );
+    }
+
+    #[test]
+    fn test_core_properties_on_smoke_tests() {
+        use std::fs;
+        use std::path::Path;
+
+        let smoke_dir = Path::new("tests/smoke");
+        if !smoke_dir.exists() {
+            eprintln!("Smoke test directory not found, skipping");
+            return;
+        }
+
+        let mut file_count = 0;
+        let mut total_violations = 0;
+
+        for entry in fs::read_dir(smoke_dir).unwrap() {
+            let entry = entry.unwrap();
+            let path = entry.path();
+
+            if path.extension().and_then(|s| s.to_str()) == Some("qmd") {
+                file_count += 1;
+                let source = fs::read_to_string(&path).unwrap_or_else(|e| {
+                    panic!("Failed to read {:?}: {}", path, e);
+                });
+
+                // Try to parse; skip files that fail (they may be intentionally malformed)
+                let mut parser = MarkdownParser::default();
+                let input_bytes = source.as_bytes();
+                let tree = match parser.parse(input_bytes, None) {
+                    Some(tree) => tree,
+                    None => {
+                        eprintln!(
+                            "Skipping {:?}: parse returned None",
+                            path.file_name().unwrap()
+                        );
+                        continue;
+                    }
+                };
+
+                let context = ASTContext::anonymous();
+                let mut error_collector = DiagnosticCollector::new();
+                let doc = match treesitter_to_pandoc(
+                    &mut std::io::sink(),
+                    &tree,
+                    input_bytes,
+                    &context,
+                    &mut error_collector,
+                ) {
+                    Ok(doc) => doc,
+                    Err(e) => {
+                        eprintln!(
+                            "Skipping {:?}: conversion failed: {:?}",
+                            path.file_name().unwrap(),
+                            e
+                        );
+                        continue;
+                    }
+                };
+
+                let violations = validate_core_properties(&doc, &source);
+
+                if !violations.is_empty() {
+                    eprintln!(
+                        "\n{:?} has {} violations:",
+                        path.file_name().unwrap(),
+                        violations.len()
+                    );
+                    for v in &violations {
+                        eprintln!("  {}", v);
+                    }
+                    total_violations += violations.len();
+                }
+            }
+        }
+
+        eprintln!("\nTested {} smoke test files", file_count);
+        assert_eq!(
+            total_violations, 0,
+            "Found {} total violations across {} files",
+            total_violations, file_count
+        );
+    }
+}
diff --git a/crates/quarto-markdown-pandoc/tests/test_metadata_source_tracking.rs b/crates/quarto-markdown-pandoc/tests/test_metadata_source_tracking.rs
index f63b3a0..89574cb 100644
--- a/crates/quarto-markdown-pandoc/tests/test_metadata_source_tracking.rs
+++ b/crates/quarto-markdown-pandoc/tests/test_metadata_source_tracking.rs
@@ -9,18 +9,16 @@ use quarto_markdown_pandoc::writers;
 
 /// Helper to resolve a SourceInfo chain to absolute file offset
 fn resolve_source_offset(source: &quarto_source_map::SourceInfo) -> usize {
-    match &source.mapping {
-        quarto_source_map::SourceMapping::Original { .. } => source.range.start.offset,
-        quarto_source_map::SourceMapping::Substring { offset, parent } => {
-            offset + resolve_source_offset(parent)
-        }
-        quarto_source_map::SourceMapping::Concat { .. } => {
-            // For concat, just use the start offset
-            source.range.start.offset
-        }
-        quarto_source_map::SourceMapping::Transformed { .. } => {
-            // For transformed, just use the start offset
-            source.range.start.offset
+    match source {
+        quarto_source_map::SourceInfo::Original { start_offset, .. } => *start_offset,
+        quarto_source_map::SourceInfo::Substring {
+            parent,
+            start_offset,
+            ..
+        } => start_offset + resolve_source_offset(parent),
+        quarto_source_map::SourceInfo::Concat { pieces } => {
+            // For concat, use the start offset of the first piece
+            pieces.first().map(|p| p.offset_in_concat).unwrap_or(0)
         }
     }
 }
diff --git a/crates/quarto-source-map/src/context.rs b/crates/quarto-source-map/src/context.rs
index 3c4100d..2486771 100644
--- a/crates/quarto-source-map/src/context.rs
+++ b/crates/quarto-source-map/src/context.rs
@@ -73,6 +73,25 @@ impl SourceContext {
         id
     }
 
+    /// Add a file with pre-computed FileInformation
+    ///
+    /// This is useful when deserializing from formats (like JSON) that include
+    /// serialized FileInformation, avoiding the need to recompute line breaks
+    /// or read from disk.
+    ///
+    /// The file is created without content (content=None), so ariadne rendering
+    /// won't work, but map_offset() will work using the provided FileInformation.
+    pub fn add_file_with_info(&mut self, path: String, file_info: FileInformation) -> FileId {
+        let id = FileId(self.files.len());
+        self.files.push(SourceFile {
+            path,
+            content: None,
+            file_info: Some(file_info),
+            metadata: FileMetadata { file_type: None },
+        });
+        id
+    }
+
     /// Get a file by ID
     pub fn get_file(&self, id: FileId) -> Option<&SourceFile> {
         self.files.get(id.0)
diff --git a/crates/quarto-source-map/src/file_info.rs b/crates/quarto-source-map/src/file_info.rs
index e890ce2..f120b1d 100644
--- a/crates/quarto-source-map/src/file_info.rs
+++ b/crates/quarto-source-map/src/file_info.rs
@@ -42,6 +42,25 @@ impl FileInformation {
         }
     }
 
+    /// Create file information from pre-computed parts
+    ///
+    /// This is useful when deserializing from formats that store
+    /// line break information directly (like JSON).
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use quarto_source_map::FileInformation;
+    ///
+    /// let info = FileInformation::from_parts(vec![6, 13], 20);
+    /// ```
+    pub fn from_parts(line_breaks: Vec<usize>, total_length: usize) -> Self {
+        FileInformation {
+            line_breaks,
+            total_length,
+        }
+    }
+
     /// Convert a byte offset to a Location with row and column
     ///
     /// Uses binary search to find which line contains the offset.
@@ -99,6 +118,11 @@ impl FileInformation {
         self.total_length
     }
 
+    /// Get the line breaks array (byte offsets of newline characters)
+    pub fn line_breaks(&self) -> &[usize] {
+        &self.line_breaks
+    }
+
     /// Get the number of lines in the file
     pub fn line_count(&self) -> usize {
         // If there are no newlines, there's 1 line
diff --git a/crates/quarto-source-map/src/lib.rs b/crates/quarto-source-map/src/lib.rs
index ec1aee6..ae8afa1 100644
--- a/crates/quarto-source-map/src/lib.rs
+++ b/crates/quarto-source-map/src/lib.rs
@@ -8,9 +8,9 @@
 //! # Overview
 //!
 //! The core types are:
-//! - [`SourceInfo`]: Tracks a location with its transformation history
-//! - [`SourceMapping`]: Enum describing how content was transformed
+//! - [`SourceInfo`]: Enum tracking a location and its transformation history
 //! - [`SourceContext`]: Manages files and provides content for mapping
+//! - [`MappedLocation`]: Result of mapping through transformation chains
 //!
 //! # Example
 //!
@@ -21,15 +21,13 @@
 //! let mut ctx = SourceContext::new();
 //! let file_id = ctx.add_file("main.qmd".into(), Some("# Hello\nWorld".into()));
 //!
-//! // Create a source location
-//! let range = Range {
-//!     start: Location { offset: 0, row: 0, column: 0 },
-//!     end: Location { offset: 7, row: 0, column: 7 },
-//! };
-//! let info = SourceInfo::original(file_id, range.clone());
+//! // Create a source location (stores only offsets)
+//! let info = SourceInfo::original(file_id, 0, 7);
 //!
-//! // Verify the source info was created correctly
-//! assert_eq!(info.range, range);
+//! // Map to get row/column information
+//! let mapped = info.map_offset(0, &ctx).unwrap();
+//! assert_eq!(mapped.location.row, 0);
+//! assert_eq!(mapped.location.column, 0);
 //! ```
 
 pub mod context;
@@ -43,6 +41,6 @@ pub mod utils;
 pub use context::{FileMetadata, SourceContext, SourceFile};
 pub use file_info::FileInformation;
 pub use mapping::MappedLocation;
-pub use source_info::{RangeMapping, SourceInfo, SourceMapping, SourcePiece};
+pub use source_info::{SourceInfo, SourcePiece};
 pub use types::{FileId, Location, Range};
 pub use utils::{line_col_to_offset, offset_to_location, range_from_offsets};
diff --git a/crates/quarto-source-map/src/mapping.rs b/crates/quarto-source-map/src/mapping.rs
index a8a9376..8b96de6 100644
--- a/crates/quarto-source-map/src/mapping.rs
+++ b/crates/quarto-source-map/src/mapping.rs
@@ -15,31 +15,37 @@ pub struct MappedLocation {
 impl SourceInfo {
     /// Map an offset in the current text back to original source
     pub fn map_offset(&self, offset: usize, ctx: &SourceContext) -> Option<MappedLocation> {
-        use crate::source_info::SourceMapping;
-
-        match &self.mapping {
-            SourceMapping::Original { file_id } => {
+        match self {
+            SourceInfo::Original {
+                file_id,
+                start_offset,
+                ..
+            } => {
                 // Direct mapping to original file
                 let file = ctx.get_file(*file_id)?;
                 let file_info = file.file_info.as_ref()?;
 
+                // Compute the absolute offset in the file
+                let absolute_offset = start_offset + offset;
+
                 // Convert offset to Location with row/column using efficient binary search
-                let location = file_info.offset_to_location(offset)?;
+                let location = file_info.offset_to_location(absolute_offset)?;
 
                 Some(MappedLocation {
                     file_id: *file_id,
                     location,
                 })
             }
-            SourceMapping::Substring {
+            SourceInfo::Substring {
                 parent,
-                offset: parent_offset,
+                start_offset,
+                ..
             } => {
                 // Map to parent coordinates and recurse
-                let parent_offset_mapped = parent_offset + offset;
-                parent.map_offset(parent_offset_mapped, ctx)
+                let parent_offset = start_offset + offset;
+                parent.map_offset(parent_offset, ctx)
             }
-            SourceMapping::Concat { pieces } => {
+            SourceInfo::Concat { pieces } => {
                 // Find which piece contains this offset
                 for piece in pieces {
                     let piece_start = piece.offset_in_concat;
@@ -53,18 +59,6 @@ impl SourceInfo {
                 }
                 None // Offset not found in any piece
             }
-            SourceMapping::Transformed { parent, mapping } => {
-                // Find the mapping that contains this offset
-                for range_mapping in mapping {
-                    if offset >= range_mapping.from_start && offset < range_mapping.from_end {
-                        // Map to parent coordinates
-                        let offset_in_range = offset - range_mapping.from_start;
-                        let parent_offset = range_mapping.to_start + offset_in_range;
-                        return parent.map_offset(parent_offset, ctx);
-                    }
-                }
-                None // Offset not found in any mapping
-            }
         }
     }
 
@@ -91,7 +85,7 @@ mod tests {
         let mut ctx = SourceContext::new();
         let file_id = ctx.add_file("test.qmd".to_string(), Some("hello\nworld".to_string()));
 
-        let info = SourceInfo::original(
+        let info = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
@@ -127,7 +121,7 @@ mod tests {
         let mut ctx = SourceContext::new();
         let file_id = ctx.add_file("test.qmd".to_string(), Some("0123456789".to_string()));
 
-        let original = SourceInfo::original(
+        let original = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
@@ -163,7 +157,7 @@ mod tests {
         let file_id1 = ctx.add_file("first.qmd".to_string(), Some("AAA".to_string()));
         let file_id2 = ctx.add_file("second.qmd".to_string(), Some("BBB".to_string()));
 
-        let info1 = SourceInfo::original(
+        let info1 = SourceInfo::from_range(
             file_id1,
             Range {
                 start: Location {
@@ -179,7 +173,7 @@ mod tests {
             },
         );
 
-        let info2 = SourceInfo::original(
+        let info2 = SourceInfo::from_range(
             file_id2,
             Range {
                 start: Location {
@@ -209,56 +203,12 @@ mod tests {
         assert_eq!(mapped.location.offset, 1);
     }
 
-    #[test]
-    fn test_map_offset_transformed() {
-        let mut ctx = SourceContext::new();
-        let file_id = ctx.add_file("test.qmd".to_string(), Some("0123456789".to_string()));
-
-        let original = SourceInfo::original(
-            file_id,
-            Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 10,
-                    row: 0,
-                    column: 10,
-                },
-            },
-        );
-
-        // Transform: map [0,3) to [5,8), skip everything else
-        use crate::source_info::RangeMapping;
-        let transformed = SourceInfo::transformed(
-            original,
-            vec![RangeMapping {
-                from_start: 0,
-                from_end: 3,
-                to_start: 5,
-                to_end: 8,
-            }],
-        );
-
-        // Map offset 0 (should map to original offset 5, which is '5')
-        let mapped = transformed.map_offset(0, &ctx).unwrap();
-        assert_eq!(mapped.file_id, file_id);
-        assert_eq!(mapped.location.offset, 5);
-
-        // Map offset 2 (should map to original offset 7, which is '7')
-        let mapped = transformed.map_offset(2, &ctx).unwrap();
-        assert_eq!(mapped.file_id, file_id);
-        assert_eq!(mapped.location.offset, 7);
-    }
-
     #[test]
     fn test_map_range() {
         let mut ctx = SourceContext::new();
         let file_id = ctx.add_file("test.qmd".to_string(), Some("hello\nworld".to_string()));
 
-        let info = SourceInfo::original(
+        let info = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
diff --git a/crates/quarto-source-map/src/source_info.rs b/crates/quarto-source-map/src/source_info.rs
index 2ff33bc..faa3192 100644
--- a/crates/quarto-source-map/src/source_info.rs
+++ b/crates/quarto-source-map/src/source_info.rs
@@ -1,35 +1,46 @@
 //! Source information with transformation tracking
 
-use crate::types::{FileId, Location, Range};
+use crate::types::{FileId, Range};
 use serde::{Deserialize, Serialize};
 use std::rc::Rc;
 
 /// Source information tracking a location and its transformation history
+///
+/// This enum stores only byte offsets. Row and column information is computed
+/// on-demand via `map_offset()` using the FileInformation line break index.
+///
+/// Design notes:
+/// - Original: Points directly to a file with byte offsets
+/// - Substring: Points to a range within a parent SourceInfo (offsets are relative to parent)
+/// - Concat: Combines multiple SourceInfo pieces (preserves provenance when coalescing text)
+///
+/// The Transformed variant was removed because it's not used in production code.
+/// Text transformations (smart quotes, em-dashes) use Original SourceInfo pointing
+/// to the pre-transformation text, accepting that the byte offsets are approximate.
 #[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-pub struct SourceInfo {
-    /// The range in the immediate/current text
-    pub range: Range,
-    /// How this range maps to its source
-    pub mapping: SourceMapping,
-}
-
-/// Describes how source content was transformed
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-pub enum SourceMapping {
+pub enum SourceInfo {
     /// Direct position in an original file
-    Original { file_id: FileId },
+    ///
+    /// Stores only byte offsets. Use `map_offset()` to get row/column information.
+    Original {
+        file_id: FileId,
+        start_offset: usize,
+        end_offset: usize,
+    },
     /// Substring extraction from a parent source
+    ///
+    /// Offsets are relative to the parent's text.
+    /// The chain of Substrings always resolves to an Original.
     Substring {
         parent: Rc<SourceInfo>,
-        offset: usize,
+        start_offset: usize,
+        end_offset: usize,
     },
     /// Concatenation of multiple sources
+    ///
+    /// Used when coalescing adjacent text nodes while preserving
+    /// the fact that they came from different source locations.
     Concat { pieces: Vec<SourcePiece> },
-    /// Transformed text with piecewise mapping
-    Transformed {
-        parent: Rc<SourceInfo>,
-        mapping: Vec<RangeMapping>,
-    },
 }
 
 /// A piece of a concatenated source
@@ -43,68 +54,44 @@ pub struct SourcePiece {
     pub length: usize,
 }
 
-/// Maps a range in transformed text to parent text
-#[derive(Debug, Clone, PartialEq, Serialize, Deserialize)]
-pub struct RangeMapping {
-    /// Start offset in transformed text
-    pub from_start: usize,
-    /// End offset in transformed text
-    pub from_end: usize,
-    /// Start offset in parent text
-    pub to_start: usize,
-    /// End offset in parent text
-    pub to_end: usize,
-}
-
 impl Default for SourceInfo {
     fn default() -> Self {
-        SourceInfo::original(
-            FileId(0),
-            Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-            },
-        )
+        SourceInfo::Original {
+            file_id: FileId(0),
+            start_offset: 0,
+            end_offset: 0,
+        }
     }
 }
 
 impl SourceInfo {
-    /// Create source info for a position in an original file
-    pub fn original(file_id: FileId, range: Range) -> Self {
-        SourceInfo {
-            range,
-            mapping: SourceMapping::Original { file_id },
+    /// Create source info for a position in an original file (from offsets)
+    pub fn original(file_id: FileId, start_offset: usize, end_offset: usize) -> Self {
+        SourceInfo::Original {
+            file_id,
+            start_offset,
+            end_offset,
+        }
+    }
+
+    /// Create source info for a position in an original file (from Range)
+    ///
+    /// This is a compatibility helper for code that still uses Range.
+    /// The row and column information in the Range is ignored; only offsets are stored.
+    pub fn from_range(file_id: FileId, range: Range) -> Self {
+        SourceInfo::Original {
+            file_id,
+            start_offset: range.start.offset,
+            end_offset: range.end.offset,
         }
     }
 
     /// Create source info for a substring extraction
     pub fn substring(parent: SourceInfo, start: usize, end: usize) -> Self {
-        let length = end - start;
-        SourceInfo {
-            range: Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: length,
-                    row: 0,
-                    column: 0,
-                },
-            },
-            mapping: SourceMapping::Substring {
-                parent: Rc::new(parent),
-                offset: start,
-            },
+        SourceInfo::Substring {
+            parent: Rc::new(parent),
+            start_offset: start,
+            end_offset: end,
         }
     }
 
@@ -130,49 +117,8 @@ impl SourceInfo {
             })
             .collect();
 
-        let total_length = cumulative_offset;
-
-        SourceInfo {
-            range: Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: total_length,
-                    row: 0,
-                    column: 0,
-                },
-            },
-            mapping: SourceMapping::Concat {
-                pieces: pieces_with_offsets,
-            },
-        }
-    }
-
-    /// Create source info for transformed text
-    pub fn transformed(parent: SourceInfo, mapping: Vec<RangeMapping>) -> Self {
-        // Find the max end offset in the transformed text
-        let total_length = mapping.iter().map(|m| m.from_end).max().unwrap_or(0);
-
-        SourceInfo {
-            range: Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: total_length,
-                    row: 0,
-                    column: 0,
-                },
-            },
-            mapping: SourceMapping::Transformed {
-                parent: Rc::new(parent),
-                mapping,
-            },
+        SourceInfo::Concat {
+            pieces: pieces_with_offsets,
         }
     }
 
@@ -181,14 +127,55 @@ impl SourceInfo {
     /// This creates a Concat mapping that preserves both sources.
     /// The resulting SourceInfo spans from the start of self to the end of other.
     pub fn combine(&self, other: &SourceInfo) -> Self {
-        let self_length = self.range.end.offset - self.range.start.offset;
-        let other_length = other.range.end.offset - other.range.start.offset;
+        let self_length = self.length();
+        let other_length = other.length();
 
         SourceInfo::concat(vec![
             (self.clone(), self_length),
             (other.clone(), other_length),
         ])
     }
+
+    /// Get the length (in bytes) represented by this SourceInfo
+    pub fn length(&self) -> usize {
+        match self {
+            SourceInfo::Original {
+                start_offset,
+                end_offset,
+                ..
+            } => end_offset - start_offset,
+            SourceInfo::Substring {
+                start_offset,
+                end_offset,
+                ..
+            } => end_offset - start_offset,
+            SourceInfo::Concat { pieces } => pieces.iter().map(|p| p.length).sum(),
+        }
+    }
+
+    /// Get the start offset for this SourceInfo
+    ///
+    /// For Original and Substring, returns the start_offset field.
+    /// For Concat, returns 0 (the concat represents a new text starting at 0).
+    pub fn start_offset(&self) -> usize {
+        match self {
+            SourceInfo::Original { start_offset, .. } => *start_offset,
+            SourceInfo::Substring { start_offset, .. } => *start_offset,
+            SourceInfo::Concat { .. } => 0,
+        }
+    }
+
+    /// Get the end offset for this SourceInfo
+    ///
+    /// For Original and Substring, returns the end_offset field.
+    /// For Concat, returns the total length.
+    pub fn end_offset(&self) -> usize {
+        match self {
+            SourceInfo::Original { end_offset, .. } => *end_offset,
+            SourceInfo::Substring { end_offset, .. } => *end_offset,
+            SourceInfo::Concat { .. } => self.length(),
+        }
+    }
 }
 
 #[cfg(test)]
@@ -212,11 +199,15 @@ mod tests {
             },
         };
 
-        let info = SourceInfo::original(file_id, range.clone());
+        let info = SourceInfo::from_range(file_id, range.clone());
 
-        assert_eq!(info.range, range);
-        match info.mapping {
-            SourceMapping::Original { file_id: mapped_id } => {
+        assert_eq!(info.start_offset(), 0);
+        assert_eq!(info.end_offset(), 10);
+        assert_eq!(info.length(), 10);
+        match info {
+            SourceInfo::Original {
+                file_id: mapped_id, ..
+            } => {
                 assert_eq!(mapped_id, file_id);
             }
             _ => panic!("Expected Original mapping"),
@@ -239,7 +230,7 @@ mod tests {
             },
         };
 
-        let info = SourceInfo::original(file_id, range);
+        let info = SourceInfo::from_range(file_id, range);
         let json = serde_json::to_string(&info).unwrap();
         let deserialized: SourceInfo = serde_json::from_str(&json).unwrap();
 
@@ -261,16 +252,22 @@ mod tests {
                 column: 100,
             },
         };
-        let parent = SourceInfo::original(file_id, parent_range);
+        let parent = SourceInfo::from_range(file_id, parent_range);
 
         let substring = SourceInfo::substring(parent, 10, 20);
 
-        assert_eq!(substring.range.start.offset, 0);
-        assert_eq!(substring.range.end.offset, 10); // length = 20 - 10 = 10
-
-        match substring.mapping {
-            SourceMapping::Substring { offset, .. } => {
-                assert_eq!(offset, 10);
+        assert_eq!(substring.start_offset(), 10);
+        assert_eq!(substring.end_offset(), 20);
+        assert_eq!(substring.length(), 10);
+
+        match substring {
+            SourceInfo::Substring {
+                start_offset,
+                end_offset,
+                ..
+            } => {
+                assert_eq!(start_offset, 10);
+                assert_eq!(end_offset, 20);
             }
             _ => panic!("Expected Substring mapping"),
         }
@@ -281,7 +278,7 @@ mod tests {
         let file_id1 = FileId(0);
         let file_id2 = FileId(1);
 
-        let info1 = SourceInfo::original(
+        let info1 = SourceInfo::from_range(
             file_id1,
             Range {
                 start: Location {
@@ -297,7 +294,7 @@ mod tests {
             },
         );
 
-        let info2 = SourceInfo::original(
+        let info2 = SourceInfo::from_range(
             file_id2,
             Range {
                 start: Location {
@@ -315,11 +312,12 @@ mod tests {
 
         let concat = SourceInfo::concat(vec![(info1, 10), (info2, 15)]);
 
-        assert_eq!(concat.range.start.offset, 0);
-        assert_eq!(concat.range.end.offset, 25); // 10 + 15
+        assert_eq!(concat.start_offset(), 0);
+        assert_eq!(concat.end_offset(), 25); // 10 + 15
+        assert_eq!(concat.length(), 25);
 
-        match concat.mapping {
-            SourceMapping::Concat { pieces } => {
+        match concat {
+            SourceInfo::Concat { pieces } => {
                 assert_eq!(pieces.len(), 2);
                 assert_eq!(pieces[0].offset_in_concat, 0);
                 assert_eq!(pieces[0].length, 10);
@@ -330,113 +328,12 @@ mod tests {
         }
     }
 
-    #[test]
-    fn test_transformed_source_info() {
-        let file_id = FileId(0);
-        let parent = SourceInfo::original(
-            file_id,
-            Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 50,
-                    row: 0,
-                    column: 50,
-                },
-            },
-        );
-
-        let mapping = vec![
-            RangeMapping {
-                from_start: 0,
-                from_end: 10,
-                to_start: 0,
-                to_end: 10,
-            },
-            RangeMapping {
-                from_start: 10,
-                from_end: 20,
-                to_start: 20,
-                to_end: 30,
-            },
-        ];
-
-        let transformed = SourceInfo::transformed(parent, mapping.clone());
-
-        assert_eq!(transformed.range.start.offset, 0);
-        assert_eq!(transformed.range.end.offset, 20); // max from_end
-
-        match transformed.mapping {
-            SourceMapping::Transformed { mapping: m, .. } => {
-                assert_eq!(m, mapping);
-            }
-            _ => panic!("Expected Transformed mapping"),
-        }
-    }
-
-    #[test]
-    fn test_nested_transformations() {
-        let file_id = FileId(0);
-        let original = SourceInfo::original(
-            file_id,
-            Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 100,
-                    row: 0,
-                    column: 100,
-                },
-            },
-        );
-
-        // Extract a substring
-        let substring = SourceInfo::substring(original, 10, 50);
-
-        // Then transform it
-        let transformed = SourceInfo::transformed(
-            substring,
-            vec![RangeMapping {
-                from_start: 0,
-                from_end: 10,
-                to_start: 0,
-                to_end: 10,
-            }],
-        );
-
-        // Verify the chain: Original -> Substring -> Transformed
-        match &transformed.mapping {
-            SourceMapping::Transformed { parent, .. } => match &parent.mapping {
-                SourceMapping::Substring {
-                    parent: grandparent,
-                    offset,
-                } => {
-                    assert_eq!(*offset, 10);
-                    match &grandparent.mapping {
-                        SourceMapping::Original { file_id: id } => {
-                            assert_eq!(*id, file_id);
-                        }
-                        _ => panic!("Expected Original at root"),
-                    }
-                }
-                _ => panic!("Expected Substring as parent"),
-            },
-            _ => panic!("Expected Transformed at top level"),
-        }
-    }
-
     #[test]
     fn test_combine_two_sources() {
         let file_id = FileId(0);
 
         // Create two separate source info objects
-        let info1 = SourceInfo::original(
+        let info1 = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
@@ -452,7 +349,7 @@ mod tests {
             },
         );
 
-        let info2 = SourceInfo::original(
+        let info2 = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
@@ -472,11 +369,12 @@ mod tests {
         let combined = info1.combine(&info2);
 
         // Should create a Concat with total length = 10 + 10 = 20
-        assert_eq!(combined.range.start.offset, 0);
-        assert_eq!(combined.range.end.offset, 20);
+        assert_eq!(combined.start_offset(), 0);
+        assert_eq!(combined.end_offset(), 20);
+        assert_eq!(combined.length(), 20);
 
-        match combined.mapping {
-            SourceMapping::Concat { pieces } => {
+        match combined {
+            SourceInfo::Concat { pieces } => {
                 assert_eq!(pieces.len(), 2);
                 assert_eq!(pieces[0].length, 10);
                 assert_eq!(pieces[0].offset_in_concat, 0);
@@ -493,7 +391,7 @@ mod tests {
         let file_id1 = FileId(5);
         let file_id2 = FileId(10);
 
-        let info1 = SourceInfo::original(
+        let info1 = SourceInfo::from_range(
             file_id1,
             Range {
                 start: Location {
@@ -509,7 +407,7 @@ mod tests {
             },
         );
 
-        let info2 = SourceInfo::original(
+        let info2 = SourceInfo::from_range(
             file_id2,
             Range {
                 start: Location {
@@ -528,19 +426,19 @@ mod tests {
         let combined = info1.combine(&info2);
 
         // Verify both sources are preserved in the Concat
-        match combined.mapping {
-            SourceMapping::Concat { pieces } => {
+        match combined {
+            SourceInfo::Concat { pieces } => {
                 assert_eq!(pieces.len(), 2);
 
                 // First piece should come from file_id1
-                match &pieces[0].source_info.mapping {
-                    SourceMapping::Original { file_id } => assert_eq!(*file_id, file_id1),
+                match &pieces[0].source_info {
+                    SourceInfo::Original { file_id, .. } => assert_eq!(*file_id, file_id1),
                     _ => panic!("Expected Original mapping for first piece"),
                 }
 
                 // Second piece should come from file_id2
-                match &pieces[1].source_info.mapping {
-                    SourceMapping::Original { file_id } => assert_eq!(*file_id, file_id2),
+                match &pieces[1].source_info {
+                    SourceInfo::Original { file_id, .. } => assert_eq!(*file_id, file_id2),
                     _ => panic!("Expected Original mapping for second piece"),
                 }
             }
@@ -565,17 +463,13 @@ mod tests {
             },
         };
 
-        let info = SourceInfo::original(file_id, range);
+        let info = SourceInfo::from_range(file_id, range);
         let json = serde_json::to_value(&info).unwrap();
 
         // Verify JSON structure
-        assert_eq!(json["range"]["start"]["offset"], 10);
-        assert_eq!(json["range"]["start"]["row"], 1);
-        assert_eq!(json["range"]["start"]["column"], 5);
-        assert_eq!(json["range"]["end"]["offset"], 50);
-        assert_eq!(json["range"]["end"]["row"], 3);
-        assert_eq!(json["range"]["end"]["column"], 10);
-        assert_eq!(json["mapping"]["Original"]["file_id"], 0);
+        assert_eq!(json["Original"]["file_id"], 0);
+        assert_eq!(json["Original"]["start_offset"], 10);
+        assert_eq!(json["Original"]["end_offset"], 50);
 
         // Verify round-trip
         let deserialized: SourceInfo = serde_json::from_value(json).unwrap();
@@ -598,22 +492,18 @@ mod tests {
                 column: 20,
             },
         };
-        let parent = SourceInfo::original(file_id, parent_range);
+        let parent = SourceInfo::from_range(file_id, parent_range);
 
         let substring = SourceInfo::substring(parent, 10, 30);
         let json = serde_json::to_value(&substring).unwrap();
 
         // Verify JSON structure
-        assert_eq!(json["range"]["start"]["offset"], 0);
-        assert_eq!(json["range"]["end"]["offset"], 20); // length = 30 - 10 = 20
-        assert_eq!(json["mapping"]["Substring"]["offset"], 10);
+        assert_eq!(json["Substring"]["start_offset"], 10);
+        assert_eq!(json["Substring"]["end_offset"], 30);
 
         // Verify parent is serialized (with Rc, it's a full copy in JSON)
-        assert!(json["mapping"]["Substring"]["parent"].is_object());
-        assert_eq!(
-            json["mapping"]["Substring"]["parent"]["mapping"]["Original"]["file_id"],
-            0
-        );
+        assert!(json["Substring"]["parent"].is_object());
+        assert_eq!(json["Substring"]["parent"]["Original"]["file_id"], 0);
 
         // Verify round-trip
         let deserialized: SourceInfo = serde_json::from_value(json).unwrap();
@@ -638,7 +528,7 @@ mod tests {
                 column: 0,
             },
         };
-        let file_info = SourceInfo::original(file_id, file_range);
+        let file_info = SourceInfo::from_range(file_id, file_range);
 
         // Level 2: YAML frontmatter (substring of file)
         let yaml_info = SourceInfo::substring(file_info, 4, 150);
@@ -649,14 +539,11 @@ mod tests {
         let json = serde_json::to_value(&value_info).unwrap();
 
         // Verify nested structure
-        assert_eq!(json["mapping"]["Substring"]["offset"], 20);
+        assert_eq!(json["Substring"]["start_offset"], 20);
+        assert_eq!(json["Substring"]["end_offset"], 35);
+        assert_eq!(json["Substring"]["parent"]["Substring"]["start_offset"], 4);
         assert_eq!(
-            json["mapping"]["Substring"]["parent"]["mapping"]["Substring"]["offset"],
-            4
-        );
-        assert_eq!(
-            json["mapping"]["Substring"]["parent"]["mapping"]["Substring"]["parent"]["mapping"]["Original"]
-                ["file_id"],
+            json["Substring"]["parent"]["Substring"]["parent"]["Original"]["file_id"],
             0
         );
 
@@ -671,7 +558,7 @@ mod tests {
         let file_id1 = FileId(0);
         let file_id2 = FileId(1);
 
-        let info1 = SourceInfo::original(
+        let info1 = SourceInfo::from_range(
             file_id1,
             Range {
                 start: Location {
@@ -687,7 +574,7 @@ mod tests {
             },
         );
 
-        let info2 = SourceInfo::original(
+        let info2 = SourceInfo::from_range(
             file_id2,
             Range {
                 start: Location {
@@ -707,127 +594,32 @@ mod tests {
         let json = serde_json::to_value(&combined).unwrap();
 
         // Verify JSON structure
-        assert!(json["mapping"]["Concat"]["pieces"].is_array());
-        let pieces = json["mapping"]["Concat"]["pieces"].as_array().unwrap();
+        assert!(json["Concat"]["pieces"].is_array());
+        let pieces = json["Concat"]["pieces"].as_array().unwrap();
         assert_eq!(pieces.len(), 2);
 
         // First piece
         assert_eq!(pieces[0]["offset_in_concat"], 0);
         assert_eq!(pieces[0]["length"], 10);
-        assert_eq!(
-            pieces[0]["source_info"]["mapping"]["Original"]["file_id"],
-            0
-        );
+        assert_eq!(pieces[0]["source_info"]["Original"]["file_id"], 0);
 
         // Second piece
         assert_eq!(pieces[1]["offset_in_concat"], 10);
         assert_eq!(pieces[1]["length"], 10);
-        assert_eq!(
-            pieces[1]["source_info"]["mapping"]["Original"]["file_id"],
-            1
-        );
+        assert_eq!(pieces[1]["source_info"]["Original"]["file_id"], 1);
 
         // Verify round-trip
         let deserialized: SourceInfo = serde_json::from_value(json).unwrap();
         assert_eq!(combined, deserialized);
     }
 
-    /// Test JSON serialization of Transformed mapping
-    #[test]
-    fn test_json_serialization_transformed() {
-        use crate::RangeMapping;
-
-        let file_id = FileId(0);
-        let parent = SourceInfo::original(
-            file_id,
-            Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 20,
-                    row: 0,
-                    column: 20,
-                },
-            },
-        );
-
-        // Create a transformed source with range mappings
-        let mappings = vec![
-            RangeMapping {
-                from_start: 0,
-                from_end: 5,
-                to_start: 0,
-                to_end: 5,
-            },
-            RangeMapping {
-                from_start: 5,
-                from_end: 10,
-                to_start: 10,
-                to_end: 15,
-            },
-        ];
-
-        let transformed = SourceInfo {
-            range: Range {
-                start: Location {
-                    offset: 0,
-                    row: 0,
-                    column: 0,
-                },
-                end: Location {
-                    offset: 10,
-                    row: 0,
-                    column: 10,
-                },
-            },
-            mapping: SourceMapping::Transformed {
-                parent: Rc::new(parent),
-                mapping: mappings.clone(),
-            },
-        };
-
-        let json = serde_json::to_value(&transformed).unwrap();
-
-        // Verify JSON structure
-        assert!(json["mapping"]["Transformed"]["mapping"].is_array());
-        let json_mappings = json["mapping"]["Transformed"]["mapping"]
-            .as_array()
-            .unwrap();
-        assert_eq!(json_mappings.len(), 2);
-
-        // Verify first mapping
-        assert_eq!(json_mappings[0]["from_start"], 0);
-        assert_eq!(json_mappings[0]["from_end"], 5);
-        assert_eq!(json_mappings[0]["to_start"], 0);
-        assert_eq!(json_mappings[0]["to_end"], 5);
-
-        // Verify second mapping
-        assert_eq!(json_mappings[1]["from_start"], 5);
-        assert_eq!(json_mappings[1]["from_end"], 10);
-        assert_eq!(json_mappings[1]["to_start"], 10);
-        assert_eq!(json_mappings[1]["to_end"], 15);
-
-        // Verify parent is serialized
-        assert_eq!(
-            json["mapping"]["Transformed"]["parent"]["mapping"]["Original"]["file_id"],
-            0
-        );
-
-        // Verify round-trip
-        let deserialized: SourceInfo = serde_json::from_value(json).unwrap();
-        assert_eq!(transformed, deserialized);
-    }
-
     /// Test JSON serialization of complex nested structure (real-world example)
     #[test]
     fn test_json_serialization_complex_nested() {
         let file_id = FileId(0);
 
         // Simulate a .qmd file structure
-        let qmd_file = SourceInfo::original(
+        let qmd_file = SourceInfo::from_range(
             file_id,
             Range {
                 start: Location {
@@ -859,7 +651,7 @@ mod tests {
 
         // Verify this complex structure serializes
         assert!(json.is_object());
-        assert!(json["mapping"]["Concat"].is_object());
+        assert!(json["Concat"].is_object());
 
         // Verify round-trip
         let deserialized: SourceInfo = serde_json::from_value(json).unwrap();
diff --git a/crates/quarto-yaml/claude-notes/implementation-plan.md b/crates/quarto-yaml/claude-notes/implementation-plan.md
index 984ba83..cc06cc3 100644
--- a/crates/quarto-yaml/claude-notes/implementation-plan.md
+++ b/crates/quarto-yaml/claude-notes/implementation-plan.md
@@ -2,7 +2,7 @@
 
 ## Overview
 
-This crate implements `YamlWithSourceInfo`, a data structure that wraps `yaml-rust2::Yaml` with source location tracking. This uses the **owned data approach** as decided in the design discussion (see `/Users/cscheid/repos/github/cscheid/kyoto/claude-notes/session-logs/2025-10-13-yaml-lifetime-vs-owned-discussion.md`).
+This crate implements `YamlWithSourceInfo`, a data structure that wraps `yaml-rust2::Yaml` with source location tracking.
 
 ## Architecture Decision: Owned Data
 
@@ -159,9 +159,3 @@ impl MarkedEventReceiver for YamlBuilder {
 3. **Unified SourceInfo** - Replace with project-wide SourceInfo type
 4. **YAML tags** - Support for !expr and custom tags
 5. **Multi-document** - Support YAML streams
-
-## References
-
-- Design document: `/Users/cscheid/repos/github/cscheid/kyoto/claude-notes/yaml-with-source-info-design.md`
-- Session log: `/Users/cscheid/repos/github/cscheid/kyoto/claude-notes/session-logs/2025-10-13-yaml-lifetime-vs-owned-discussion.md`
-- rust-analyzer patterns: `/Users/cscheid/repos/github/cscheid/kyoto/claude-notes/rust-analyzer-owned-data-patterns.md`
diff --git a/crates/quarto-yaml/src/error.rs b/crates/quarto-yaml/src/error.rs
index 842fb1a..a1e5fb5 100644
--- a/crates/quarto-yaml/src/error.rs
+++ b/crates/quarto-yaml/src/error.rs
@@ -30,38 +30,31 @@ impl fmt::Display for Error {
         match self {
             Error::ParseError { message, location } => {
                 write!(f, "Parse error: {}", message)?;
-                if let Some(loc) = location {
-                    // Display with 1-indexed row/column
-                    write!(
-                        f,
-                        " at {}:{}",
-                        loc.range.start.row + 1,
-                        loc.range.start.column + 1
-                    )?;
+                // TODO: Proper location display requires SourceContext to map offsets to row/column.
+                // For now, we only show the error message without location details.
+                // To fix: refactor Error type to carry SourceContext or resolve locations before creating errors.
+                if let Some(_loc) = location {
+                    // Location information available but cannot display without SourceContext
                 }
                 Ok(())
             }
             Error::UnexpectedEof { location } => {
                 write!(f, "Unexpected end of input")?;
-                if let Some(loc) = location {
-                    write!(
-                        f,
-                        " at {}:{}",
-                        loc.range.start.row + 1,
-                        loc.range.start.column + 1
-                    )?;
+                // TODO: Proper location display requires SourceContext to map offsets to row/column.
+                // For now, we only show the error message without location details.
+                // To fix: refactor Error type to carry SourceContext or resolve locations before creating errors.
+                if let Some(_loc) = location {
+                    // Location information available but cannot display without SourceContext
                 }
                 Ok(())
             }
             Error::InvalidStructure { message, location } => {
                 write!(f, "Invalid YAML structure: {}", message)?;
-                if let Some(loc) = location {
-                    write!(
-                        f,
-                        " at {}:{}",
-                        loc.range.start.row + 1,
-                        loc.range.start.column + 1
-                    )?;
+                // TODO: Proper location display requires SourceContext to map offsets to row/column.
+                // For now, we only show the error message without location details.
+                // To fix: refactor Error type to carry SourceContext or resolve locations before creating errors.
+                if let Some(_loc) = location {
+                    // Location information available but cannot display without SourceContext
                 }
                 Ok(())
             }
diff --git a/crates/quarto-yaml/src/lib.rs b/crates/quarto-yaml/src/lib.rs
index ae9d644..98f56c3 100644
--- a/crates/quarto-yaml/src/lib.rs
+++ b/crates/quarto-yaml/src/lib.rs
@@ -28,7 +28,7 @@
 //! let yaml = parse(content).unwrap();
 //! // Access with source location tracking
 //! if let Some(title) = yaml.get_hash_value("title") {
-//!     println!("Title at offset {}", title.source_info.range.start.offset);
+//!     println!("Title at offset {}", title.source_info.start_offset());
 //! }
 //! ```
 
diff --git a/crates/quarto-yaml/src/parser.rs b/crates/quarto-yaml/src/parser.rs
index 7218099..f990c41 100644
--- a/crates/quarto-yaml/src/parser.rs
+++ b/crates/quarto-yaml/src/parser.rs
@@ -38,7 +38,7 @@ pub fn parse(content: &str) -> Result<YamlWithSourceInfo> {
 ///
 /// let yaml = parse_file("title: My Document", "config.yaml").unwrap();
 /// // Filename tracking will be added in a future update
-/// assert!(yaml.source_info.range.end.offset > 0);
+/// assert!(yaml.source_info.end_offset() > 0);
 /// ```
 ///
 /// # Errors
@@ -67,7 +67,7 @@ pub fn parse_file(content: &str, filename: &str) -> Result<YamlWithSourceInfo> {
 /// use quarto_source_map::{FileId, Location, Range};
 ///
 /// // Create parent source info for a .qmd file
-/// let parent = SourceInfo::original(
+/// let parent = SourceInfo::from_range(
 ///     FileId(1),
 ///     Range {
 ///         start: Location { offset: 0, row: 0, column: 0 },
@@ -107,7 +107,7 @@ fn parse_impl(
 
             // Create SourceInfo for the entire file content
             use quarto_source_map::{Location, Range};
-            SourceInfo::original(
+            SourceInfo::from_range(
                 file_id,
                 Range {
                     start: Location {
@@ -135,6 +135,52 @@ fn parse_impl(
     builder.result()
 }
 
+/// Helper function to create a contiguous span from start to end positions.
+/// This is used for entry_span which should cover from key start to value end.
+fn create_contiguous_span(start_info: &SourceInfo, end_info: &SourceInfo) -> SourceInfo {
+    // Extract the actual start and end offsets, handling the different SourceInfo variants
+    match (start_info, end_info) {
+        (
+            SourceInfo::Original {
+                file_id: start_file,
+                start_offset: start,
+                ..
+            },
+            SourceInfo::Original {
+                file_id: end_file,
+                end_offset: end,
+                ..
+            },
+        ) => {
+            // Both are Original from the same file - create a single Original span
+            assert_eq!(
+                start_file, end_file,
+                "Key and value must be from the same file"
+            );
+            SourceInfo::original(*start_file, *start, *end)
+        }
+        (
+            SourceInfo::Substring {
+                parent: start_parent,
+                start_offset: start,
+                ..
+            },
+            SourceInfo::Substring {
+                end_offset: end, ..
+            },
+        ) => {
+            // Both are Substrings - they should have the same parent
+            // Use the first parent (they should be equivalent even if not the same Rc)
+            SourceInfo::substring((**start_parent).clone(), *start, *end)
+        }
+        _ => {
+            // Mixed types or Concat - fall back to combine which creates a Concat
+            // This shouldn't happen in normal YAML parsing but handle it gracefully
+            start_info.combine(end_info)
+        }
+    }
+}
+
 /// Builder that implements MarkedEventReceiver to construct YamlWithSourceInfo.
 struct YamlBuilder<'a> {
     /// The source text being parsed (reserved for future use in accurate scalar length computation)
@@ -224,7 +270,7 @@ impl<'a> YamlBuilder<'a> {
             let start_row = marker.line(); // yaml-rust2 uses 0-based
             let start_column = marker.col(); // yaml-rust2 uses 0-based
 
-            SourceInfo::original(
+            SourceInfo::from_range(
                 quarto_source_map::FileId(0), // Dummy FileId for now
                 Range {
                     start: Location {
@@ -345,14 +391,8 @@ impl<'a> MarkedEventReceiver for YamlBuilder<'a> {
                         let value_span = value.source_info.clone();
 
                         // Entry span from key start to value end
-                        use quarto_source_map::Range;
-                        let entry_span = SourceInfo::original(
-                            quarto_source_map::FileId(0), // Dummy FileId
-                            Range {
-                                start: key_span.range.start.clone(),
-                                end: value_span.range.end.clone(),
-                            },
-                        );
+                        // Create a contiguous span (not a Concat) from key start to value end
+                        let entry_span = create_contiguous_span(&key_span, &value_span);
 
                         hash_entries.push(YamlHashEntry::new(
                             key.clone(),
@@ -497,21 +537,21 @@ project:
 
         // Check that source info is present
         // Note: row/column are 0-indexed in the new system
-        assert!(yaml.source_info.range.start.offset < yaml.source_info.range.end.offset);
+        assert!(yaml.source_info.start_offset() < yaml.source_info.end_offset());
 
         let title = yaml.get_hash_value("title").unwrap();
         // Verify the title value has a valid range
-        assert!(title.source_info.range.start.offset < title.source_info.range.end.offset);
+        assert!(title.source_info.start_offset() < title.source_info.end_offset());
     }
 
     #[test]
     fn test_parse_with_filename() {
         let yaml = parse_file("title: Test", "config.yaml").unwrap();
-        assert!(yaml.source_info.range.end.offset > 0);
+        assert!(yaml.source_info.end_offset() > 0);
 
         // Verify that we're now using Substring mapping for files
-        match &yaml.source_info.mapping {
-            quarto_source_map::SourceMapping::Substring { .. } => {
+        match &yaml.source_info {
+            SourceInfo::Substring { .. } => {
                 // Expected: Substring mapping to parent file
             }
             _ => panic!("Expected Substring mapping for file parsing"),
@@ -523,7 +563,7 @@ project:
         use quarto_source_map::{FileId, Location, Range};
 
         // Simulate extracting YAML from a .qmd file at offset 100-150
-        let parent = SourceInfo::original(
+        let parent = SourceInfo::from_range(
             FileId(42),
             Range {
                 start: Location {
@@ -543,14 +583,11 @@ project:
         let yaml = parse_with_parent(yaml_content, parent).unwrap();
 
         // Verify root has Substring mapping
-        match &yaml.source_info.mapping {
-            quarto_source_map::SourceMapping::Substring {
-                parent: p,
-                offset: _,
-            } => {
+        match &yaml.source_info {
+            SourceInfo::Substring { parent: p, .. } => {
                 // Parent should point to our original parent
-                match &p.mapping {
-                    quarto_source_map::SourceMapping::Original { file_id } => {
+                match p.as_ref() {
+                    SourceInfo::Original { file_id, .. } => {
                         assert_eq!(file_id.0, 42);
                     }
                     _ => panic!("Expected parent to have Original mapping"),
@@ -565,7 +602,7 @@ project:
         use quarto_source_map::{FileId, Location, Range};
 
         // Parent file
-        let parent = SourceInfo::original(
+        let parent = SourceInfo::from_range(
             FileId(1),
             Range {
                 start: Location {
@@ -602,30 +639,15 @@ project:
             .expect("authors key not found");
 
         // All should have Substring mappings
-        assert!(matches!(
-            project.source_info.mapping,
-            quarto_source_map::SourceMapping::Substring { .. }
-        ));
-        assert!(matches!(
-            title.source_info.mapping,
-            quarto_source_map::SourceMapping::Substring { .. }
-        ));
-        assert!(matches!(
-            authors.source_info.mapping,
-            quarto_source_map::SourceMapping::Substring { .. }
-        ));
+        assert!(matches!(project.source_info, SourceInfo::Substring { .. }));
+        assert!(matches!(title.source_info, SourceInfo::Substring { .. }));
+        assert!(matches!(authors.source_info, SourceInfo::Substring { .. }));
 
         // Array elements should also have Substring mappings
         if let Some(items) = authors.as_array() {
             assert_eq!(items.len(), 2);
-            assert!(matches!(
-                items[0].source_info.mapping,
-                quarto_source_map::SourceMapping::Substring { .. }
-            ));
-            assert!(matches!(
-                items[1].source_info.mapping,
-                quarto_source_map::SourceMapping::Substring { .. }
-            ));
+            assert!(matches!(items[0].source_info, SourceInfo::Substring { .. }));
+            assert!(matches!(items[1].source_info, SourceInfo::Substring { .. }));
         } else {
             panic!("Expected array for authors");
         }
@@ -637,7 +659,7 @@ project:
 
         // Parent document
         let parent_content = "---\ntitle: Test\nauthor: John\n---\n\nDocument content";
-        let parent = SourceInfo::original(
+        let parent = SourceInfo::from_range(
             FileId(1),
             Range {
                 start: Location {
@@ -661,16 +683,16 @@ project:
         let title = yaml.get_hash_value("title").expect("title not found");
 
         // Verify the title has a valid substring range
-        match &title.source_info.mapping {
-            quarto_source_map::SourceMapping::Substring { offset, .. } => {
+        match &title.source_info {
+            SourceInfo::Substring { start_offset, .. } => {
                 // Offset should be relative to the yaml_content string
-                assert!(*offset < yaml_content.len());
+                assert!(*start_offset < yaml_content.len());
             }
             _ => panic!("Expected Substring mapping for title"),
         }
 
         // Check that range makes sense
-        assert!(title.source_info.range.start.offset < title.source_info.range.end.offset);
+        assert!(title.source_info.start_offset() < title.source_info.end_offset());
     }
 
     #[test]
@@ -678,8 +700,8 @@ project:
         // Parse without filename or parent - should use Original mapping
         let yaml = parse("title: Test").unwrap();
 
-        match &yaml.source_info.mapping {
-            quarto_source_map::SourceMapping::Original { file_id } => {
+        match &yaml.source_info {
+            SourceInfo::Original { file_id, .. } => {
                 assert_eq!(file_id.0, 0); // Anonymous FileId
             }
             _ => panic!("Expected Original mapping for anonymous parse"),
@@ -689,13 +711,19 @@ project:
     /// Helper function to resolve a SourceInfo through the mapping chain to get
     /// the absolute offset in the original file.
     fn resolve_to_original_offset(info: &SourceInfo) -> (usize, quarto_source_map::FileId) {
-        match &info.mapping {
-            quarto_source_map::SourceMapping::Original { file_id } => {
-                (info.range.start.offset, *file_id)
-            }
-            quarto_source_map::SourceMapping::Substring { parent, offset } => {
+        match info {
+            SourceInfo::Original {
+                file_id,
+                start_offset,
+                ..
+            } => (*start_offset, *file_id),
+            SourceInfo::Substring {
+                parent,
+                start_offset,
+                ..
+            } => {
                 let (parent_offset, file_id) = resolve_to_original_offset(parent);
-                (parent_offset + offset, file_id)
+                (parent_offset + start_offset, file_id)
             }
             _ => panic!("Unsupported mapping type for offset resolution"),
         }
@@ -718,13 +746,13 @@ project:
 
         // Verify key location
         assert_eq!(hello_entry.key.yaml.as_str(), Some("hello"));
-        let key_offset = hello_entry.key_span.range.start.offset;
+        let key_offset = hello_entry.key_span.start_offset();
         let key_str = &yaml_content[key_offset..key_offset + 5];
         assert_eq!(key_str, "hello", "Key location should point to 'hello'");
 
         // Verify value location
         assert_eq!(hello_entry.value.yaml.as_str(), Some("world"));
-        let value_offset = hello_entry.value_span.range.start.offset;
+        let value_offset = hello_entry.value_span.start_offset();
         let value_str = &yaml_content[value_offset..value_offset + 5];
         assert_eq!(value_str, "world", "Value location should point to 'world'");
 
@@ -740,11 +768,11 @@ project:
             .find(|e| e.key.yaml.as_str() == Some("foo"))
             .expect("Should have 'foo' key");
 
-        let foo_key_offset = foo_entry.key_span.range.start.offset;
+        let foo_key_offset = foo_entry.key_span.start_offset();
         let foo_key_str = &yaml_content[foo_key_offset..foo_key_offset + 3];
         assert_eq!(foo_key_str, "foo", "Key location should point to 'foo'");
 
-        let bar_value_offset = foo_entry.value_span.range.start.offset;
+        let bar_value_offset = foo_entry.value_span.start_offset();
         let bar_value_str = &yaml_content[bar_value_offset..bar_value_offset + 3];
         assert_eq!(bar_value_str, "bar", "Value location should point to 'bar'");
 
@@ -754,7 +782,7 @@ project:
             .find(|e| e.key.yaml.as_str() == Some("count"))
             .expect("Should have 'count' key");
 
-        let count_key_offset = count_entry.key_span.range.start.offset;
+        let count_key_offset = count_entry.key_span.start_offset();
         let count_key_str = &yaml_content[count_key_offset..count_key_offset + 5];
         assert_eq!(
             count_key_str, "count",
@@ -762,18 +790,18 @@ project:
         );
 
         assert_eq!(count_entry.value.yaml.as_i64(), Some(42));
-        let count_value_offset = count_entry.value_span.range.start.offset;
+        let count_value_offset = count_entry.value_span.start_offset();
         let count_value_str = &yaml_content[count_value_offset..count_value_offset + 2];
         assert_eq!(count_value_str, "42", "Value location should point to '42'");
 
         // Test 4: Verify entry spans include both key and value
         // The entry span should start at the key and end after the value
         assert!(
-            hello_entry.entry_span.range.start.offset <= key_offset,
+            hello_entry.entry_span.start_offset() <= key_offset,
             "Entry span should start at or before the key"
         );
         assert!(
-            hello_entry.entry_span.range.end.offset >= value_offset + 5,
+            hello_entry.entry_span.end_offset() >= value_offset + 5,
             "Entry span should end at or after the value"
         );
     }
@@ -816,7 +844,7 @@ We used the following approach...
         let yaml_content = yaml_match.as_str();
 
         // Create parent SourceInfo for the entire .qmd file
-        let parent = SourceInfo::original(
+        let parent = SourceInfo::from_range(
             FileId(123), // Simulated FileId for test.qmd
             Range {
                 start: Location {
@@ -844,23 +872,28 @@ We used the following approach...
         assert_eq!(title.yaml.as_str(), Some("My Research Paper"));
 
         // Verify that the title's location maps back through the substring chain
-        match &title.source_info.mapping {
-            quarto_source_map::SourceMapping::Substring { parent: p, offset } => {
+        match &title.source_info {
+            SourceInfo::Substring {
+                parent: p,
+                start_offset,
+                ..
+            } => {
                 // The offset should be within the YAML content
-                assert!(*offset < yaml_content.len());
+                assert!(*start_offset < yaml_content.len());
 
                 // The parent should be another Substring pointing to the .qmd file
-                match &p.mapping {
-                    quarto_source_map::SourceMapping::Substring {
+                match p.as_ref() {
+                    SourceInfo::Substring {
                         parent: grandparent,
-                        offset: yaml_offset,
+                        start_offset: yaml_offset,
+                        ..
                     } => {
                         // This should point to the original .qmd file
                         assert_eq!(*yaml_offset, yaml_start);
 
                         // Grandparent should be the Original .qmd file
-                        match &grandparent.mapping {
-                            quarto_source_map::SourceMapping::Original { file_id } => {
+                        match grandparent.as_ref() {
+                            SourceInfo::Original { file_id, .. } => {
                                 assert_eq!(file_id.0, 123);
                             }
                             _ => panic!("Expected Original mapping for .qmd file"),
@@ -883,8 +916,8 @@ We used the following approach...
         assert_eq!(theme.yaml.as_str(), Some("cosmo"));
 
         // The theme value should also have Substring mapping through the chain
-        match &theme.source_info.mapping {
-            quarto_source_map::SourceMapping::Substring { .. } => {
+        match &theme.source_info {
+            SourceInfo::Substring { .. } => {
                 // Good - it has substring mapping
             }
             _ => panic!("Expected Substring mapping for deeply nested theme value"),
diff --git a/crates/quarto-yaml/src/yaml_with_source_info.rs b/crates/quarto-yaml/src/yaml_with_source_info.rs
index ee758a1..04dfa28 100644
--- a/crates/quarto-yaml/src/yaml_with_source_info.rs
+++ b/crates/quarto-yaml/src/yaml_with_source_info.rs
@@ -28,7 +28,7 @@ use yaml_rust2::Yaml;
 /// let yaml = parse("title: My Document").unwrap();
 /// if let Some(title) = yaml.get_hash_value("title") {
 ///     println!("Title: {:?}", title.yaml);
-///     println!("Location: offset {}", title.source_info.range.start.offset);
+///     println!("Location: offset {}", title.source_info.start_offset());
 /// }
 /// ```
 #[derive(Debug, Clone)]
diff --git a/docs/writers/json.qmd b/docs/writers/json.qmd
index 97e2438..8582545 100644
--- a/docs/writers/json.qmd
+++ b/docs/writers/json.qmd
@@ -14,7 +14,7 @@ The JSON output contains three main sections:
   "meta": { /* metadata */ },
   "blocks": [ /* block elements */ ],
   "astContext": {
-    "filenames": [ /* array of source files */ ],
+    "files": [ /* array of source file information */ ],
     "sourceInfoPool": [ /* source location data */ ]
   }
 }
@@ -35,9 +35,15 @@ Unlike Pandoc, `quarto-markdown-pandoc` tracks the exact source location of ever
 ```json
 {
   "astContext": {
-    "filenames": ["example.qmd"],
+    "files": [
+      {
+        "name": "example.qmd",
+        "line_breaks": [11],
+        "total_length": 11
+      }
+    ],
     "sourceInfoPool": [
-      {"r": [0, 0, 0, 4, 0, 4], "t": 0, "d": 0}
+      {"r": [0, 5], "t": 0, "d": 0}
     ]
   },
   "blocks": [
@@ -59,21 +65,21 @@ The `"s": 0` field means "look up source info at index 0 in the pool".
 Each entry in the `sourceInfoPool` array has this compact format:
 
 ```json
-{"r": [start_offset, start_row, start_col, end_offset, end_row, end_col], "t": type, "d": data}
+{"r": [start_offset, end_offset], "t": type, "d": data}
 ```
 
 ### Fields
 
-- **`r`** (range): 6-element array `[start_offset, start_row, start_col, end_offset, end_row, end_col]`
-  - All positions are 0-indexed
-  - `offset` is byte offset from start of source
-  - `row` and `col` are line and column numbers
+- **`r`** (range): 2-element array `[start_offset, end_offset]`
+  - Byte offsets from the start of the relevant source
+  - For Original: absolute offsets in the source file
+  - For Substring: relative offsets within the parent source
+  - Row and column information is computed on-demand from the file's line break index
 
 - **`t`** (type): Integer indicating the source mapping type
   - `0` = Original (direct position in source file)
   - `1` = Substring (extracted from a parent source)
   - `2` = Concat (multiple sources joined together)
-  - `3` = Transformed (source that was modified with explicit mapping)
 
 - **`d`** (data): Type-specific data (see below)
 
@@ -82,7 +88,7 @@ Each entry in the `sourceInfoPool` array has this compact format:
 Represents text directly from a source file.
 
 ```json
-{"r": [0, 0, 0, 10, 0, 10], "t": 0, "d": 0}
+{"r": [0, 5], "t": 0, "d": 0}
 ```
 
 - **`d`**: The file ID (index into `astContext.filenames`)
@@ -94,46 +100,30 @@ Represents text directly from a source file.
 Represents a substring extracted from another source.
 
 ```json
-{"r": [0, 0, 0, 5, 0, 5], "t": 1, "d": [3, 10]}
+{"r": [4, 17], "t": 1, "d": 3}
 ```
 
-- **`d`**: `[parent_id, offset]`
-  - `parent_id`: Index of the parent source in the pool
-  - `offset`: Byte offset within the parent where this substring starts
+- **`d`**: Index of the parent source in the pool
+- **`r`**: `[start_offset, end_offset]` within the parent source (relative offsets)
 
-**Example**: A 5-byte substring starting at byte 10 of source #3 (e.g., extracting YAML value from frontmatter).
+**Example**: A 13-byte substring from bytes 4-17 of source #3 (e.g., extracting YAML value from frontmatter).
 
 ### Type 2: Concat
 
 Represents multiple sources concatenated together.
 
 ```json
-{"r": [0, 0, 0, 10, 0, 10], "t": 2, "d": [[1, 0, 5], [2, 5, 5]]}
+{"r": [0, 10], "t": 2, "d": [[1, 0, 5], [2, 5, 5]]}
 ```
 
 - **`d`**: Array of pieces, where each piece is `[source_info_id, offset_in_concat, length]`
   - `source_info_id`: Index of this piece's source in the pool
-  - `offset_in_concat`: Where this piece starts in the concatenated result
+  - `offset_in_concat`: Where this piece starts in the concatenated result (0-based)
   - `length`: Length of this piece in bytes
+- **`r`**: `[0, total_length]` - the concatenated result spans from 0 to the sum of all piece lengths
 
 **Example**: Joining sources #1 (5 bytes) and #2 (5 bytes) to create a 10-byte result.
 
-### Type 3: Transformed
-
-Represents source text that was transformed (e.g., entity decoding, shortcode expansion) with explicit range mappings.
-
-```json
-{"r": [0, 0, 0, 8, 0, 8], "t": 3, "d": [4, [[0, 4, 0, 4], [4, 8, 6, 10]]]}
-```
-
-- **`d`**: `[parent_id, range_mappings]`
-  - `parent_id`: Index of the parent source in the pool
-  - `range_mappings`: Array of `[from_start, from_end, to_start, to_end]`
-    - `from_start`, `from_end`: Range in the transformed text (this source)
-    - `to_start`, `to_end`: Corresponding range in the parent text
-
-**Example**: 8 bytes of transformed text derived from bytes 0-4 and 6-10 of source #4.
-
 ## Complete Example
 
 ```json
@@ -152,12 +142,18 @@ Represents source text that was transformed (e.g., entity decoding, shortcode ex
     }
   ],
   "astContext": {
-    "filenames": ["example.qmd"],
+    "files": [
+      {
+        "name": "example.qmd",
+        "line_breaks": [],
+        "total_length": 11
+      }
+    ],
     "sourceInfoPool": [
-      {"r": [0, 0, 0, 5, 0, 5], "t": 0, "d": 0},
-      {"r": [5, 0, 5, 6, 0, 6], "t": 0, "d": 0},
-      {"r": [6, 0, 6, 11, 0, 11], "t": 0, "d": 0},
-      {"r": [0, 0, 0, 11, 0, 11], "t": 2, "d": [[0, 0, 5], [1, 5, 1], [2, 6, 5]]}
+      {"r": [0, 5], "t": 0, "d": 0},
+      {"r": [5, 6], "t": 0, "d": 0},
+      {"r": [6, 11], "t": 0, "d": 0},
+      {"r": [0, 11], "t": 2, "d": [[0, 0, 5], [1, 5, 1], [2, 6, 5]]}
     ]
   }
 }
@@ -165,13 +161,34 @@ Represents source text that was transformed (e.g., entity decoding, shortcode ex
 
 ### Explanation
 
-- Pool entry 0: "Hello" at bytes 0-5
-- Pool entry 1: Space at byte 5-6
-- Pool entry 2: "world" at bytes 6-11
-- Pool entry 3: Concatenation of all three pieces
+- Pool entry 0: "Hello" at bytes 0-5 (Original)
+- Pool entry 1: Space at bytes 5-6 (Original)
+- Pool entry 2: "world" at bytes 6-11 (Original)
+- Pool entry 3: Concatenation of all three pieces (Concat)
 - The Para block references entry 3 (the full concatenated range)
 - Each inline element references its individual piece
 
+## File Information
+
+The `files` array in `astContext` contains information about each source file. Each entry has:
+
+```json
+{
+  "name": "example.qmd",        // Source file path
+  "line_breaks": [6, 13, 20],   // Byte offsets of each newline character
+  "total_length": 25            // Total file size in bytes
+}
+```
+
+The `line_breaks` and `total_length` fields allow JSON consumers to convert byte offsets to row/column positions without needing access to the original source files.
+
+To convert a byte offset to (row, column):
+1. Use binary search on `line_breaks` to find which line contains the offset
+2. The row is the index where the offset would be inserted
+3. The column is the offset minus the start of that line
+
+This information is self-contained in the JSON, so consumers don't need to reopen source files
+
 ## Pandoc compatibility
 
 For compatibility with tools expecting Pandoc JSON, either ignore the `"s"` fields and `astContext` section (that's what Pandoc will do) or remove them from the JSON object ahead of time.