feat(server): add annotation to tool macro (#184)

skip serializing the tool annotations if none, fixes mcp inspector

crates/rmcp/src/model/tool.rs

@@ -37,11 +37,13 @@ pub struct Tool {
 #[cfg_attr(feature = "schemars", derive(schemars::JsonSchema))]
 pub struct ToolAnnotations {
     /// A human-readable title for the tool.
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub title: Option<String>,
 
     /// If true, the tool does not modify its environment.
     ///
     /// Default: false
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub read_only_hint: Option<bool>,
 
     /// If true, the tool may perform destructive updates to its environment.
@@ -51,6 +53,7 @@ pub struct ToolAnnotations {
     ///
     /// Default: true
     /// A human-readable description of the tool's purpose.
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub destructive_hint: Option<bool>,
 
     /// If true, calling the tool repeatedly with the same arguments
@@ -59,6 +62,7 @@ pub struct ToolAnnotations {
     /// (This property is meaningful only when `readOnlyHint == false`)
     ///
     /// Default: false.
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub idempotent_hint: Option<bool>,
 
     /// If true, this tool may interact with an "open world" of external
@@ -67,6 +71,7 @@ pub struct ToolAnnotations {
     /// of a memory tool is not.
     ///
     /// Default: true
+    #[serde(skip_serializing_if = "Option::is_none")]
     pub open_world_hint: Option<bool>,
 }
 

crates/rmcp/tests/test_tool_macro_annotations.rs

@@ -0,0 +1,59 @@
+#[cfg(test)]
+mod tests {
+    use rmcp::{ServerHandler, tool};
+
+    #[derive(Debug, Clone, Default)]
+    pub struct AnnotatedServer {}
+
+    impl AnnotatedServer {
+        // Tool with inline comments for documentation
+        /// Direct annotation test tool
+        /// This is used to test tool annotations
+        #[tool(
+            name = "direct-annotated-tool",
+            annotations = {
+                title: "Annotated Tool", 
+                readOnlyHint: true
+            }
+        )]
+        pub async fn direct_annotated_tool(&self, #[tool(param)] input: String) -> String {
+            format!("Direct: {}", input)
+        }
+    }
+
+    impl ServerHandler for AnnotatedServer {
+        async fn call_tool(
+            &self,
+            request: rmcp::model::CallToolRequestParam,
+            context: rmcp::service::RequestContext<rmcp::RoleServer>,
+        ) -> Result<rmcp::model::CallToolResult, rmcp::Error> {
+            let tcc = rmcp::handler::server::tool::ToolCallContext::new(self, request, context);
+            match tcc.name() {
+                "direct-annotated-tool" => Self::direct_annotated_tool_tool_call(tcc).await,
+                _ => Err(rmcp::Error::invalid_params("method not found", None)),
+            }
+        }
+    }
+
+    #[test]
+    fn test_direct_tool_attributes() {
+        // Get the tool definition
+        let tool = AnnotatedServer::direct_annotated_tool_tool_attr();
+
+        // Verify basic properties
+        assert_eq!(tool.name, "direct-annotated-tool");
+
+        // Verify description is extracted from doc comments
+        assert!(tool.description.is_some());
+        assert!(
+            tool.description
+                .as_ref()
+                .unwrap()
+                .contains("Direct annotation test tool")
+        );
+
+        let annotations = tool.annotations.unwrap();
+        assert_eq!(annotations.title.as_ref().unwrap(), "Annotated Tool");
+        assert_eq!(annotations.read_only_hint, Some(true));
+    }
+}