feat(cli): When invoked with only a schema file (no instances), validates the schema against its meta-schema

CHANGELOG.md

@@ -6,7 +6,9 @@
 
 - **CLI**: Structured `--output flag|list|hierarchical` modes now stream newline-delimited JSON records with schema/instance metadata plus JSON Schema Output v1 payloads (default `text` output remains human-readable).
 - **CLI**: `--errors-only` flag to suppress successful validation output and only show failures.
+- **CLI**: When invoked with only a schema file (no instances), validates the schema against its meta-schema. [#804](https://github.com/Stranger6667/jsonschema/issues/804)
 - New `Validator::evaluate()` API exposes JSON Schema Output v1 (flag/list/hierarchical) reports along with iterator helpers for annotations and errors.
+- `meta::validator_for()` function to build validators for meta-schema validation with full `Validator` API access.
 - `Validator` now implements `Clone`. [#809](https://github.com/Stranger6667/jsonschema/issues/809)
 
 ### Removed

crates/jsonschema-cli/src/main.rs

@@ -181,6 +181,65 @@ fn path_to_uri(path: &std::path::Path) -> String {
     result
 }
 
+fn output_schema_validation(
+    schema_path: &Path,
+    schema_json: &serde_json::Value,
+    output: Output,
+    errors_only: bool,
+) -> Result<bool, Box<dyn std::error::Error>> {
+    let meta_validator = jsonschema::meta::validator_for(schema_json)?;
+    let evaluation = meta_validator.evaluate(schema_json);
+    let flag_output = evaluation.flag();
+
+    // Skip valid schemas if errors_only is enabled
+    if !(errors_only && flag_output.valid) {
+        let schema_display = schema_path.to_string_lossy().to_string();
+        let output_format = output.as_str();
+        let payload = match output {
+            Output::Text => unreachable!("text mode should not call this function"),
+            Output::Flag => serde_json::to_value(flag_output)?,
+            Output::List => serde_json::to_value(evaluation.list())?,
+            Output::Hierarchical => serde_json::to_value(evaluation.hierarchical())?,
+        };
+
+        let record = json!({
+            "output": output_format,
+            "schema": &schema_display,
+            "payload": payload,
+        });
+        println!("{}", serde_json::to_string(&record)?);
+    }
+
+    Ok(flag_output.valid)
+}
+
+fn validate_schema_meta(
+    schema_path: &Path,
+    output: Output,
+    errors_only: bool,
+) -> Result<bool, Box<dyn std::error::Error>> {
+    let schema_json = read_json(schema_path)??;
+
+    if matches!(output, Output::Text) {
+        // Text output mode
+        match jsonschema::meta::validate(&schema_json) {
+            Ok(()) => {
+                if !errors_only {
+                    println!("Schema is valid");
+                }
+                Ok(true)
+            }
+            Err(error) => {
+                println!("Schema is invalid. Error: {error}");
+                Ok(false)
+            }
+        }
+    } else {
+        // Structured output modes using evaluate API
+        output_schema_validation(schema_path, &schema_json, output, errors_only)
+    }
+}
+
 fn validate_instances(
     instances: &[PathBuf],
     schema_path: &Path,
@@ -255,7 +314,12 @@ fn validate_instances(
             }
         }
         Err(error) => {
-            println!("Schema is invalid. Error: {error}");
+            if matches!(output, Output::Text) {
+                println!("Schema is invalid. Error: {error}");
+            } else {
+                // Schema compilation failed - validate the schema itself to get structured output
+                output_schema_validation(schema_path, &schema_json, output, errors_only)?;
+            }
             success = false;
         }
     }
@@ -274,7 +338,7 @@ fn main() -> ExitCode {
         if let Some(instances) = config.instances {
             // - Some(true)  if --assert-format
             // - Some(false) if --no-assert-format
-            // - None        if neither (use builder’s default)
+            // - None        if neither (use builder's default)
             let assert_format = config.assert_format.or(config.no_assert_format);
             return match validate_instances(
                 &instances,
@@ -292,6 +356,15 @@ fn main() -> ExitCode {
                 }
             };
         }
+        // No instances provided - validate the schema itself
+        return match validate_schema_meta(&schema, config.output, config.errors_only) {
+            Ok(true) => ExitCode::SUCCESS,
+            Ok(false) => ExitCode::FAILURE,
+            Err(error) => {
+                println!("Error: {error}");
+                ExitCode::FAILURE
+            }
+        };
     }
     ExitCode::SUCCESS
 }

crates/jsonschema-cli/tests/cli.rs

@@ -713,3 +713,174 @@ fn test_errors_only_structured_output() {
     assert_eq!(records[0]["instance"], invalid);
     assert_eq!(records[0]["payload"]["valid"], false);
 }
+
+#[test]
+fn test_validate_valid_schema() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(&dir, "schema.json", r#"{"type": "string"}"#);
+
+    let mut cmd = cli();
+    cmd.arg(&schema);
+    let output = cmd.output().unwrap();
+    assert!(output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(stdout.contains("Schema is valid"));
+}
+
+#[test]
+fn test_validate_invalid_schema() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+
+    let mut cmd = cli();
+    cmd.arg(&schema);
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(stdout.contains("Schema is invalid"));
+}
+
+#[test]
+fn test_instance_validation_with_invalid_schema_structured_output() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+    let instance = create_temp_file(&dir, "instance.json", "42");
+
+    let mut cmd = cli();
+    cmd.arg(&schema)
+        .arg("--instance")
+        .arg(&instance)
+        .arg("--output")
+        .arg("flag");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let json: serde_json::Value = serde_json::from_str(&stdout).expect("Should be valid JSON");
+
+    assert_eq!(json["output"], "flag");
+    assert_eq!(json["payload"]["valid"], false);
+    assert!(json["schema"].as_str().unwrap().ends_with("schema.json"));
+}
+
+#[test]
+fn test_instance_validation_with_invalid_schema_list_output() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+    let instance = create_temp_file(&dir, "instance.json", "42");
+
+    let mut cmd = cli();
+    cmd.arg(&schema)
+        .arg("--instance")
+        .arg(&instance)
+        .arg("--output")
+        .arg("list");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let json: serde_json::Value = serde_json::from_str(&stdout).expect("Should be valid JSON");
+
+    assert_eq!(json["output"], "list");
+    assert_eq!(json["payload"]["valid"], false);
+    assert!(json["schema"].as_str().unwrap().ends_with("schema.json"));
+}
+
+#[test]
+fn test_instance_validation_with_invalid_schema_hierarchical_output() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+    let instance = create_temp_file(&dir, "instance.json", "42");
+
+    let mut cmd = cli();
+    cmd.arg(&schema)
+        .arg("--instance")
+        .arg(&instance)
+        .arg("--output")
+        .arg("hierarchical");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let json: serde_json::Value = serde_json::from_str(&stdout).expect("Should be valid JSON");
+
+    assert_eq!(json["output"], "hierarchical");
+    assert_eq!(json["payload"]["valid"], false);
+    assert!(json["schema"].as_str().unwrap().ends_with("schema.json"));
+}
+
+#[test]
+fn test_validate_invalid_schema_list_output() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+
+    let mut cmd = cli();
+    cmd.arg(&schema).arg("--output").arg("list");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let json: serde_json::Value = serde_json::from_str(&stdout).expect("Should be valid JSON");
+
+    assert_eq!(json["output"], "list");
+    assert_eq!(json["payload"]["valid"], false);
+    assert!(json["schema"].as_str().unwrap().ends_with("schema.json"));
+}
+
+#[test]
+fn test_validate_invalid_schema_hierarchical_output() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(
+        &dir,
+        "schema.json",
+        r#"{"type": "invalid_type", "minimum": "not a number"}"#,
+    );
+
+    let mut cmd = cli();
+    cmd.arg(&schema).arg("--output").arg("hierarchical");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    let json: serde_json::Value = serde_json::from_str(&stdout).expect("Should be valid JSON");
+
+    assert_eq!(json["output"], "hierarchical");
+    assert_eq!(json["payload"]["valid"], false);
+    assert!(json["schema"].as_str().unwrap().ends_with("schema.json"));
+}
+
+#[test]
+fn test_validate_schema_with_json_parse_error() {
+    let dir = tempdir().unwrap();
+    let schema = create_temp_file(&dir, "schema.json", r#"{"type": "string"#);
+
+    let mut cmd = cli();
+    cmd.arg(&schema).arg("--output").arg("flag");
+    let output = cmd.output().unwrap();
+    assert!(!output.status.success());
+
+    let stdout = String::from_utf8_lossy(&output.stdout);
+    assert!(stdout.contains("Error:"));
+}

crates/jsonschema-cli/tests/snapshots/cli__no_instances.snap

@@ -2,4 +2,4 @@
 source: crates/jsonschema-cli/tests/cli.rs
 expression: "String::from_utf8_lossy(&output.stdout)"
 ---
-
+Schema is valid