feat(meta): add _meta field to prompts, resources and paginated result (#558)

Author: pbezglasny

crates/rmcp-macros/src/prompt.rs

@@ -18,6 +18,8 @@ pub struct PromptAttribute {
     pub arguments: Option<Expr>,
     /// Optional icons for the prompt
     pub icons: Option<Expr>,
+    /// Optional metadata for the prompt
+    pub meta: Option<Expr>,
 }
 
 pub struct ResolvedPromptAttribute {
@@ -26,6 +28,7 @@ pub struct ResolvedPromptAttribute {
     pub description: Option<Expr>,
     pub arguments: Expr,
     pub icons: Option<Expr>,
+    pub meta: Option<Expr>,
 }
 
 impl ResolvedPromptAttribute {
@@ -36,6 +39,7 @@ impl ResolvedPromptAttribute {
             arguments,
             title,
             icons,
+            meta,
         } = self;
         let description = if let Some(description) = description {
             quote! { Some(#description.into()) }
@@ -52,6 +56,11 @@ impl ResolvedPromptAttribute {
         } else {
             quote! { None }
         };
+        let meta = if let Some(meta) = meta {
+            quote! { Some(#meta) }
+        } else {
+            quote! { None }
+        };
         let tokens = quote! {
             pub fn #fn_ident() -> rmcp::model::Prompt {
                 rmcp::model::Prompt {
@@ -60,6 +69,7 @@ impl ResolvedPromptAttribute {
                     arguments: #arguments,
                     title: #title,
                     icons: #icons,
+                    meta: #meta,
                 }
             }
         };
@@ -114,6 +124,7 @@ pub fn prompt(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream>
         arguments: arguments.clone(),
         title: attribute.title,
         icons: attribute.icons,
+        meta: attribute.meta,
     };
     let prompt_attr_fn = resolved_prompt_attr.into_fn(prompt_attr_fn_ident.clone())?;
 

crates/rmcp-macros/src/prompt_handler.rs

@@ -7,6 +7,7 @@ use syn::{Expr, ImplItem, ItemImpl, parse_quote};
 #[darling(default)]
 pub struct PromptHandlerAttribute {
     pub router: Option<Expr>,
+    pub meta: Option<Expr>,
 }
 
 pub fn prompt_handler(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
@@ -40,6 +41,12 @@ pub fn prompt_handler(attr: TokenStream, input: TokenStream) -> syn::Result<Toke
         }
     };
 
+    let meta = if let Some(meta) = attribute.meta {
+        quote! { Some(#meta) }
+    } else {
+        quote! { None }
+    };
+
     // Add list_prompts implementation
     let list_prompts_impl: ImplItem = parse_quote! {
         async fn list_prompts(
@@ -50,6 +57,7 @@ pub fn prompt_handler(attr: TokenStream, input: TokenStream) -> syn::Result<Toke
             let prompts = #router_expr.list_all();
             Ok(ListPromptsResult {
                 prompts,
+                meta: #meta,
                 next_cursor: None,
             })
         }

crates/rmcp-macros/src/tool_handler.rs

@@ -7,6 +7,7 @@ use syn::{Expr, ImplItem, ItemImpl};
 #[darling(default)]
 pub struct ToolHandlerAttribute {
     pub router: Expr,
+    pub meta: Option<Expr>,
 }
 
 impl Default for ToolHandlerAttribute {
@@ -16,13 +17,14 @@ impl Default for ToolHandlerAttribute {
                 self.tool_router
             })
             .unwrap(),
+            meta: None,
         }
     }
 }
 
 pub fn tool_handler(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
     let attr_args = NestedMeta::parse_meta_list(attr)?;
-    let ToolHandlerAttribute { router } = ToolHandlerAttribute::from_list(&attr_args)?;
+    let ToolHandlerAttribute { router, meta } = ToolHandlerAttribute::from_list(&attr_args)?;
     let mut item_impl = syn::parse2::<ItemImpl>(input.clone())?;
     let tool_call_fn = quote! {
         async fn call_tool(
@@ -34,13 +36,24 @@ pub fn tool_handler(attr: TokenStream, input: TokenStream) -> syn::Result<TokenS
             #router.call(tcc).await
         }
     };
+
+    let result_meta = if let Some(meta) = meta {
+        quote! { Some(#meta) }
+    } else {
+        quote! { None }
+    };
+
     let tool_list_fn = quote! {
         async fn list_tools(
             &self,
             _request: Option<rmcp::model::PaginatedRequestParam>,
             _context: rmcp::service::RequestContext<rmcp::RoleServer>,
         ) -> Result<rmcp::model::ListToolsResult, rmcp::ErrorData> {
-            Ok(rmcp::model::ListToolsResult::with_all_items(#router.list_all()))
+            Ok(rmcp::model::ListToolsResult{
+                tools: #router.list_all(),
+                meta: #result_meta,
+                next_cursor: None,
+            })
         }
     };
     let tool_call_fn = syn::parse2::<ImplItem>(tool_call_fn)?;

crates/rmcp/src/handler/server/router.rs

@@ -102,7 +102,7 @@ where
                 let tools = self.tool_router.list_all();
                 Ok(ServerResult::ListToolsResult(ListToolsResult {
                     tools,
-                    next_cursor: None,
+                    ..Default::default()
                 }))
             }
             ClientRequest::GetPromptRequest(request) => {
@@ -125,7 +125,7 @@ where
                 let prompts = self.prompt_router.list_all();
                 Ok(ServerResult::ListPromptsResult(ListPromptsResult {
                     prompts,
-                    next_cursor: None,
+                    ..Default::default()
                 }))
             }
             rest => self.service.handle_request(rest, context).await,

crates/rmcp/src/model.rs

@@ -828,6 +828,8 @@ macro_rules! paginated_result {
         #[serde(rename_all = "camelCase")]
         #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
         pub struct $t {
+            #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+            pub meta: Option<Meta>,
             #[serde(skip_serializing_if = "Option::is_none")]
             pub next_cursor: Option<Cursor>,
             pub $i_item: $t_item,
@@ -838,6 +840,7 @@ macro_rules! paginated_result {
                 items: $t_item,
             ) -> Self {
                 Self {
+                    meta: None,
                     next_cursor: None,
                     $i_item: items,
                 }

crates/rmcp/src/model/content.rs

@@ -258,6 +258,7 @@ mod tests {
             mime_type: Some("text/plain".to_string()),
             size: Some(100),
             icons: None,
+            meta: None,
         });
 
         let json = serde_json::to_string(&resource_link).unwrap();

crates/rmcp/src/model/prompt.rs

@@ -2,7 +2,7 @@ use base64::engine::{Engine, general_purpose::STANDARD as BASE64_STANDARD};
 use serde::{Deserialize, Serialize};
 
 use super::{
-    AnnotateAble, Annotations, Icon, RawEmbeddedResource, RawImageContent,
+    AnnotateAble, Annotations, Icon, Meta, RawEmbeddedResource, RawImageContent,
     content::{EmbeddedResource, ImageContent},
     resource::ResourceContents,
 };
@@ -25,6 +25,9 @@ pub struct Prompt {
     /// Optional list of icons for the prompt
     #[serde(skip_serializing_if = "Option::is_none")]
     pub icons: Option<Vec<Icon>>,
+    /// Optional additional metadata for this prompt
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<Meta>,
 }
 
 impl Prompt {
@@ -44,6 +47,7 @@ impl Prompt {
             description: description.map(Into::into),
             arguments,
             icons: None,
+            meta: None,
         }
     }
 }

crates/rmcp/src/model/resource.rs

@@ -29,6 +29,9 @@ pub struct RawResource {
     /// Optional list of icons for the resource
     #[serde(skip_serializing_if = "Option::is_none")]
     pub icons: Option<Vec<Icon>>,
+    /// Optional additional metadata for this resource
+    #[serde(rename = "_meta", skip_serializing_if = "Option::is_none")]
+    pub meta: Option<Meta>,
 }
 
 pub type Resource = Annotated<RawResource>;
@@ -95,6 +98,7 @@ impl RawResource {
             mime_type: None,
             size: None,
             icons: None,
+            meta: None,
         }
     }
 }
@@ -115,6 +119,7 @@ mod tests {
             mime_type: Some("text/plain".to_string()),
             size: Some(100),
             icons: None,
+            meta: None,
         };
 
         let json = serde_json::to_string(&resource).unwrap();

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema.json

@@ -992,6 +992,14 @@
       "description": "Represents a resource in the extension with metadata",
       "type": "object",
       "properties": {
+        "_meta": {
+          "description": "Optional additional metadata for this resource",
+          "type": [
+            "object",
+            "null"
+          ],
+          "additionalProperties": true
+        },
         "description": {
           "description": "Optional description of the resource",
           "type": [

crates/rmcp/tests/test_message_schema/client_json_rpc_message_schema_current.json

@@ -992,6 +992,14 @@
       "description": "Represents a resource in the extension with metadata",
       "type": "object",
       "properties": {
+        "_meta": {
+          "description": "Optional additional metadata for this resource",
+          "type": [
+            "object",
+            "null"
+          ],
+          "additionalProperties": true
+        },
         "description": {
           "description": "Optional description of the resource",
           "type": [