fix: strip and validate tool outputSchema and inputSchema (#860)

* fix: remove unnecessary fields from tools' outputSchema

* fix: validate input schema root type per MCP spec

crates/rmcp/tests/test_list_tools_result.rs

@@ -1,6 +1,7 @@
 #![cfg(all(feature = "server", feature = "macros", not(feature = "local")))]
 
 use rmcp::{
+    Json,
     handler::server::wrapper::Parameters,
     model::{ListToolsResult, NumberOrString, ServerJsonRpcMessage, ServerResult},
 };
@@ -14,10 +15,17 @@ struct AddRequest {
     b: f64,
 }
 
+/// Result of adding two numbers.
+#[derive(Debug, serde::Serialize, schemars::JsonSchema)]
+struct AddResult {
+    /// The sum of the two numbers.
+    sum: f64,
+}
+
 /// Add two numbers.
 #[rmcp::tool]
-fn add(Parameters(AddRequest { a, b }): Parameters<AddRequest>) -> String {
-    (a + b).to_string()
+fn add(Parameters(AddRequest { a, b }): Parameters<AddRequest>) -> Json<AddResult> {
+    Json(AddResult { sum: a + b })
 }
 
 #[test]
@@ -27,7 +35,7 @@ fn list_tools_result_matches_expected_json() {
     let expected: serde_json::Value =
         serde_json::from_slice(&expected_json).expect("invalid expected JSON fixture");
 
-    assert_eq!(add(Parameters(AddRequest { a: 1.0, b: 2.0 })), "3");
+    assert_eq!(add(Parameters(AddRequest { a: 1.0, b: 2.0 })).0.sum, 3.0);
 
     let result = ListToolsResult::with_all_items(vec![add_tool_attr()]);
     let response = ServerJsonRpcMessage::response(

crates/rmcp/tests/test_list_tools_result/list_tools_result.json

@@ -23,6 +23,20 @@
                         "a",
                         "b"
                     ]
+                },
+                "outputSchema": {
+                    "$schema": "https://json-schema.org/draft/2020-12/schema",
+                    "type": "object",
+                    "properties": {
+                        "sum": {
+                            "description": "The sum of the two numbers.",
+                            "format": "double",
+                            "type": "number"
+                        }
+                    },
+                    "required": [
+                        "sum"
+                    ]
                 }
             }
         ]

crates/rmcp/tests/test_structured_output.rs

@@ -28,6 +28,16 @@ pub struct UserInfo {
     pub age: u32,
 }
 
+#[derive(Serialize, Deserialize, JsonSchema)]
+pub struct GreetingRequest {
+    pub name: String,
+}
+
+#[derive(Serialize, Deserialize, JsonSchema)]
+pub struct GetUserRequest {
+    pub user_id: String,
+}
+
 #[tool_handler(router = self.tool_router)]
 impl ServerHandler for TestServer {}
 
@@ -64,14 +74,17 @@ impl TestServer {
 
     /// Tool that returns regular string output
     #[tool(name = "get-greeting", description = "Get a greeting")]
-    pub async fn get_greeting(&self, name: Parameters<String>) -> String {
-        format!("Hello, {}!", name.0)
+    pub async fn get_greeting(&self, params: Parameters<GreetingRequest>) -> String {
+        format!("Hello, {}!", params.0.name)
     }
 
     /// Tool that returns structured user info
     #[tool(name = "get-user", description = "Get user info")]
-    pub async fn get_user(&self, user_id: Parameters<String>) -> Result<Json<UserInfo>, String> {
-        if user_id.0 == "123" {
+    pub async fn get_user(
+        &self,
+        params: Parameters<GetUserRequest>,
+    ) -> Result<Json<UserInfo>, String> {
+        if params.0.user_id == "123" {
             Ok(Json(UserInfo {
                 name: "Alice".to_string(),
                 age: 30,