fix: strip and validate tool outputSchema and inputSchema#860

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alexhancock merged 2 commits into from
Jun 2, 2026
Merged

fix: strip and validate tool outputSchema and inputSchema #860

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7018860
fix: remove unnecessary fields from tools' outputSchema
DaleSeo May 28, 2026
d8f81f4
fix: validate input schema root type per MCP spec
DaleSeo May 28, 2026
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2 changes: 1 addition & 1 deletion README.md
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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down
7 changes: 7 additions & 0 deletions crates/rmcp-macros/src/tool.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
// if found, use the Parameters schema
syn::parse2::<Expr>(quote! {
rmcp::handler::server::common::schema_for_input::<#params_ty>()
.unwrap_or_else(|e| {
panic!(
"Invalid input schema for `{}`: {}",
std::any::type_name::<#params_ty>(),
e
)
})
})?
} else {
// if not found, use a default empty JSON schema object
Expand Down
142 changes: 89 additions & 53 deletions crates/rmcp/src/handler/server/common.rs
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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
any::TypeId,
collections::HashMap,
sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
let generator = settings.into_generator();
let schema = generator.into_root_schema_for::<T>();
let object = serde_json::to_value(schema).expect("failed to serialize schema");
let object = match object {
serde_json::Value::Object(object) => object,
_ => panic!(
"Schema serialization produced non-object value: expected JSON object but got {:?}",
object
),
let serde_json::Value::Object(object) = object else {
panic!(
"Schema serialization produced non-object value: expected JSON object but got {object:?}"
);
};
let schema = Arc::new(object);
cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
})
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
match raw.get("type") {
Some(serde_json::Value::String(t)) if t == "object" => {
let mut object = raw.as_ref().clone();
object.remove("title");
object.remove("description");
Ok(Arc::new(object))
}
Some(serde_json::Value::String(t)) => Err(format!(
"MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
)),
None => Err(format!(
"Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
)),
Some(other) => Err(format!(
"Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
)),
}
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
thread_local! {
static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
};
CACHE_FOR_INPUT.with(|cache| {
if let Some(schema) = cache
if let Some(result) = cache
.read()
.expect("input schema cache lock poisoned")
.get(&TypeId::of::<T>())
{
schema.clone()
} else {
let mut schema = schema_for_type::<T>().as_ref().clone();

// Remove unnecessary top-level fields
schema.remove("title");
schema.remove("description");

let schema = Arc::new(schema);
cache
.write()
.expect("input schema cache lock poisoned")
.insert(TypeId::of::<T>(), schema.clone());

schema
return result.clone();
}
let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
cache
.write()
.expect("input schema cache lock poisoned")
.insert(TypeId::of::<T>(), result.clone());
result
})
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
std::sync::Arc::new(
serde_json::json!({
"type": "object",
"properties": {}
})
.as_object()
.unwrap()
.clone(),
)
static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
let mut object = JsonObject::new();
object.insert("type".into(), serde_json::json!("object"));
object.insert("properties".into(), serde_json::json!({}));
Arc::new(object)
});
EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
thread_local! {
static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
return result.clone();
}

// Generate and validate schema
let schema = schema_for_type::<T>();
let result = match schema.get("type") {
Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
Some(serde_json::Value::String(t)) => Err(format!(
"MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
t
)),
None => Err(
"Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
),
Some(other) => Err(format!(
"Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
other
)),
};
// Generate, validate, and strip unnecessary top-level fields
let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

// Cache the result (both success and error cases)
cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
let result = schema_for_output::<TestObject>();
assert!(result.is_ok(),);
}

#[test]
fn test_schema_for_output_strips_top_level_title() {
let schema = schema_for_output::<TestObject>().unwrap();
assert!(!schema.contains_key("title"));
}

#[test]
fn test_schema_for_output_strips_top_level_description() {
let schema = schema_for_output::<TestObject>().unwrap();
assert!(!schema.contains_key("description"));
}

#[test]
fn test_schema_for_input_rejects_primitive() {
let result = schema_for_input::<i32>();
assert!(result.is_err());
}

#[test]
fn test_schema_for_input_accepts_object() {
let result = schema_for_input::<TestObject>();
assert!(result.is_ok());
}

#[test]
fn test_schema_for_input_strips_top_level_title() {
let schema = schema_for_input::<TestObject>().unwrap();
assert!(!schema.contains_key("title"));
}

#[test]
fn test_schema_for_input_strips_top_level_description() {
let schema = schema_for_input::<TestObject>().unwrap();
assert!(!schema.contains_key("description"));
}
}
11 changes: 9 additions & 2 deletions crates/rmcp/src/handler/server/router/tool.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
attr: Tool::new(
name.into(),
"",
schema_for_input::<crate::model::JsonObject>(),
schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
panic!("Invalid input schema for JsonObject: {e}");
}),
),
call: self,
_marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
self
}
pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
self.attr.input_schema = schema_for_input::<T>();
self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
panic!(
"Invalid input schema for `{}`: {e}",
std::any::type_name::<T>()
)
});
self
}
pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down
9 changes: 8 additions & 1 deletion crates/rmcp/src/handler/server/router/tool/tool_traits.rs
View file
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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
/// If the tool does not have any parameters, you should override this methods to return [`None`],
/// and when invoked, the parameter will get default values.
fn input_schema() -> Option<Arc<JsonObject>> {
Some(schema_for_input::<Parameters<Self::Parameter>>())
Some(
schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
panic!(
"Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
std::any::type_name::<Self::Parameter>(),
);
}),
)
}

/// Json schema for tool output.
Expand Down
3 changes: 2 additions & 1 deletion crates/rmcp/src/model/tool.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
/// Set the input schema using a type that implements JsonSchema
#[cfg(feature = "server")]
pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
.unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
self
}

Expand Down
14 changes: 11 additions & 3 deletions crates/rmcp/tests/test_list_tools_result.rs
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Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down
14 changes: 14 additions & 0 deletions crates/rmcp/tests/test_list_tools_result/list_tools_result.json
View file
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Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
]
}
}
]
Expand Down
21 changes: 17 additions & 4 deletions crates/rmcp/tests/test_structured_output.rs
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Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down
, 'i'); if (__m === '*' || __re.test(location.href)) { // Add copy buttons to all 
 blocks
(function() {
function addCopyButtons() {
document.querySelectorAll('pre code').forEach(function(codeBlock) {
if (codeBlock.parentElement.hasAttribute('data-copy-added')) return;
codeBlock.parentElement.setAttribute('data-copy-added', 'true');
var btn = document.createElement('button');
btn.textContent = 'Copy';
btn.style.cssText = 'position:absolute;top:4px;right:4px;padding:2px 8px;font-size:11px;background:#4ecdc4;border:none;border-radius:4px;color:#1a1a2e;cursor:pointer;opacity:0.7;transition:opacity 0.2s;';
btn.onmouseover = function() { this.style.opacity = '1'; };
btn.onmouseout = function() { this.style.opacity = '0.7'; };
btn.onclick = function() {
navigator.clipboard.writeText(codeBlock.textContent).then(function() {
btn.textContent = 'Copied!';
setTimeout(function() { btn.textContent = 'Copy'; }, 1500);
});
};
codeBlock.parentElement.style.position = 'relative';
codeBlock.parentElement.appendChild(btn);
});
}
addCopyButtons();
// Re-run on dynamic content
var observer = new MutationObserver(addCopyButtons);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Add Copy Buttons to Code Blocks]', __e); }
})();
(function(){
try {
var __m = "github.com";
var __re = new RegExp('^' + "github\\.com" + '

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fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

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Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

View file


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Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Force GitHub README to respect dark mode
(function() {
var style = document.createElement('style');
style.textContent = '
.markdown-body {
color-scheme: dark light;
}
.markdown-body pre { background: #161b22 !important; }
.markdown-body code { background: rgba(110, 118, 129, 0.4) !important; }
.markdown-body table th, .markdown-body table td { border-color: #30363d !important; }
.markdown-body img { background: #0d1117; }
.markdown-body blockquote { border-left-color: #8b949e; }
.markdown-body hr { border-color: #30363d; }
';
document.head.appendChild(style);
})();
}
} catch(__e) { console.warn('[Userscript:GitHub Dark Mode README Fix]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

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Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Highlight search terms from Google/DuckDuckGo/Bing referrer
(function() {
var ref = document.referrer;
var terms = [];
if (ref.includes('google.com') || ref.includes('duckduckgo.com') || ref.includes('bing.com')) {
var url = new URL(ref);
var q = url.searchParams.get('q') || url.searchParams.get('p');
if (q) {
terms = q.split(/\s+/).filter(function(t) { return t.length > 2; });
}
}
if (terms.length === 0) return;
var style = document.createElement('style');
style.textContent = '.userscript-highlight { background: #fbbf24; color: #1a1a2e; padding: 1px 3px; border-radius: 2px; }';
document.head.appendChild(style);
function highlight(node) {
if (node.nodeType === 3) { // text node
var text = node.textContent;
var found = false;
terms.forEach(function(term) {
var regex = new RegExp('(' + term.replace(/[.*+?^${}()|[\]\\]/g, '\\') + ')', 'gi');
if (regex.test(text)) {
found = true;
var frag = document.createDocumentFragment();
var parts = text.split(regex);
parts.forEach(function(part, i) {
if (i % 2 === 0) {
frag.appendChild(document.createTextNode(part));
} else {
var span = document.createElement('span');
span.className = 'userscript-highlight';
span.textContent = part;
frag.appendChild(span);
}
});
node.parentNode.replaceChild(frag, node);
}
});
} else if (node.nodeType === 1 && node.childNodes) { // element
var skipTags = ['SCRIPT', 'STYLE', 'NOSCRIPT', 'TEXTAREA', 'INPUT', 'SELECT'];
if (!skipTags.includes(node.tagName)) {
Array.from(node.childNodes).forEach(highlight);
}
}
}
highlight(document.body);
// Re-highlight on dynamic content
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1 || node.nodeType === 3) highlight(node);
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Highlight Search Terms]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

from

Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

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Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Strip utm_, fbclid, gclid, etc. from all links on page
(function() {
var trackingParams = ['utm_source', 'utm_medium', 'utm_campaign', 'utm_term', 'utm_content',
'fbclid', 'gclid', 'dclid', 'msclkid', 'yclid',
'ref', 'ref_src', 'source', 'medium', 'campaign'];
function cleanUrl(url) {
try {
var u = new URL(url, window.location.origin);
var changed = false;
trackingParams.forEach(function(p) {
if (u.searchParams.has(p)) {
u.searchParams.delete(p);
changed = true;
}
});
return changed ? u.toString() : url;
} catch (e) {
return url;
}
}
function cleanLinks() {
document.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
cleanLinks();
var observer = new MutationObserver(function(mutations) {
mutations.forEach(function(m) {
m.addedNodes.forEach(function(node) {
if (node.nodeType === 1) {
if (node.tagName === 'A') cleanLinks();
node.querySelectorAll('a[href]').forEach(function(a) {
var clean = cleanUrl(a.href);
if (clean !== a.href) a.href = clean;
});
}
});
});
});
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:Remove Tracking Parameters from Links]', __e); }
})();
(function(){
try {
var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '

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fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

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Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
(function() {
function tryTheater() {
var btn = document.querySelector('button[aria-label="Theater mode"], ytd-player #player button[title="Theater mode"]');
if (btn && !btn.classList.contains('activated')) {
btn.click();
}
}
// Try immediately
tryTheater();
// Try after navigation (SPA)
var lastUrl = location.href;
setInterval(function() {
if (location.href !== lastUrl) {
lastUrl = location.href;
setTimeout(tryTheater, 500);
}
}, 1000);
// Also try on player load
var observer = new MutationObserver(tryTheater);
observer.observe(document.body, { childList: true, subtree: true });
})();
}
} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

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fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

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Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Remove or un-stick sticky/fixed headers that block content
(function() {
function unstick() {
document.querySelectorAll('header, nav, [role="banner"], .header, .navbar, .sticky, .fixed-top, [style*="position: fixed"], [style*="position:sticky"]').forEach(function(el) {
if (el.style.position === 'fixed' || el.style.position === 'sticky' || getComputedStyle(el).position === 'fixed' || getComputedStyle(el).position === 'sticky') {
el.style.position = 'static';
el.style.top = 'auto';
el.style.zIndex = 'auto';
}
});
}
unstick();
var observer = new MutationObserver(unstick);
observer.observe(document.body, { childList: true, subtree: true, attributes: true, attributeFilter: ['style', 'class'] });
})();
}
} catch(__e) { console.warn('[Userscript:Kill Sticky Headers]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '

Skip to content
fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

from

Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

View file


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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

Expand Down

14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

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Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
Expand Down

14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
Expand Down

21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
Expand Down

, 'i');
if (__m === '*' || __re.test(location.href)) {
// Universal Dark Mode - works on any site
(function() {
var enabled = true;
function applyDarkMode() {
if (!enabled) return;
// Create style element if it doesn't exist
var style = document.getElementById('universal-dark-mode-style');
if (!style) {
style = document.createElement('style');
style.id = 'universal-dark-mode-style';
document.head.appendChild(style);
}
// Dark mode CSS - inverts colors but preserves images/video
style.textContent = '
/* Invert everything except media */
html {
filter: invert(1) hue-rotate(180deg) !important;
background: #1a1a2e !important;
}
/* Restore images, videos, iframes, canvas */
img, video, iframe, canvas, svg, picture, [style*="background-image"] {
filter: invert(1) hue-rotate(180deg) !important;
}
/* Preserve specific elements that should not be inverted */
.no-dark-mode, .no-dark-mode *,
[data-theme="light"], [data-theme="light"],
.ace_editor, .ace_editor *,
.CodeMirror, .CodeMirror *,
.monaco-editor, .monaco-editor *,
.markdown-body pre, .markdown-body pre *,
.highlight, .highlight *,
pre code, pre code * {
filter: none !important;
}
/* Fix common UI elements */
.modal, .popup, .dropdown-menu, .tooltip, .popover {
filter: invert(1) hue-rotate(180deg) !important;
background: #2d2d44 !important;
border-color: #444 !important;
}
/* Scrollbars */
::-webkit-scrollbar { background: #1a1a2e !important; }
::-webkit-scrollbar-thumb { background: #444 !important; }
::-webkit-scrollbar-thumb:hover { background: #555 !important; }
/* Selection */
::selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
::-moz-selection { background: #4ecdc4 !important; color: #1a1a2e !important; }
';
}
function removeDarkMode() {
var style = document.getElementById('universal-dark-mode-style');
if (style) style.remove();
}
// Toggle with Alt+Shift+D
document.addEventListener('keydown', function(e) {
if (e.altKey && e.shiftKey && e.key === 'D') {
e.preventDefault();
enabled = !enabled;
if (enabled) {
applyDarkMode();
console.log('[Universal Dark Mode] Enabled');
} else {
removeDarkMode();
console.log('[Universal Dark Mode] Disabled');
}
}
});
// Apply on load
applyDarkMode();
// Re-apply on dynamic content
var observer = new MutationObserver(function(mutations) {
if (enabled && !document.getElementById('universal-dark-mode-style')) {
applyDarkMode();
}
});
observer.observe(document.head, { childList: true });
console.log('[Universal Dark Mode] Loaded - Press Alt+Shift+D to toggle');
})();
}
} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
})();
})();

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fix: strip and validate tool outputSchema and inputSchema#860

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 Merged

alexhancock
merged 2 commits into

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Jun 2, 2026
 Merged


fix: strip and validate tool outputSchema and inputSchema
#860
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7018860

fix: remove unnecessary fields from tools' outputSchema


DaleSeo May 28, 2026
d8f81f4

fix: validate input schema root type per MCP spec


DaleSeo May 28, 2026

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2 changes: 1 addition & 1 deletion
README.md

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Original file line numberDiff line numberDiff line change
Expand Up@@ -169,7 +169,7 @@ async fn main() -> anyhow::Result<()> {
}
```

The generated tool `inputSchema` is derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.
The generated tool `inputSchema` and `outputSchema` are derived from the fields of `T`. The type name and documentation on `T` are ignored; only field names, field types, and field documentation are used.

When you need custom server metadata or multiple capabilities (tools + prompts), use explicit `#[tool_handler]`:

Expand Down

7 changes: 7 additions & 0 deletions
crates/rmcp-macros/src/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -232,6 +232,13 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
 // if found, use the Parameters schema
 syn::parse2::<Expr>(quote! {
 rmcp::handler::server::common::schema_for_input::<#params_ty>()
 .unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {}",
 std::any::type_name::<#params_ty>(),
 e
 )
 })
 })?
 } else {
 // if not found, use a default empty JSON schema object
Expand Down

142 changes: 89 additions & 53 deletions
crates/rmcp/src/handler/server/common.rs

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Original file line numberDiff line numberDiff line change
@@ -1,6 +1,10 @@
//! Common utilities shared between tool and prompt handlers

use std::{any::TypeId, collections::HashMap, sync::Arc};
use std::{
 any::TypeId,
 collections::HashMap,
 sync::{Arc, LazyLock},
};

use schemars::JsonSchema;

Expand DownExpand Up@@ -30,12 +34,10 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 let generator = settings.into_generator();
 let schema = generator.into_root_schema_for::<T>();
 let object = serde_json::to_value(schema).expect("failed to serialize schema");
 let object = match object {
 serde_json::Value::Object(object) => object,
 _ => panic!(
 "Schema serialization produced non-object value: expected JSON object but got {:?}",
 object
 ),
 let serde_json::Value::Object(object) = object else {
 panic!(
 "Schema serialization produced non-object value: expected JSON object but got {object:?}"
 );
 };
 let schema = Arc::new(object);
 cache
Expand All@@ -48,51 +50,63 @@ pub fn schema_for_type<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
 })
}

/// Generate a JSON schema for inputSchema (does not need "title" or "description" fields for the top-level object)
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Arc<JsonObject> {
/// Validate that the schema root is `type: "object"` (per MCP spec) and strip top-level
/// `title`/`description` (the wrapper type name and doc, which are noise to the LLM).
fn validate_and_strip(raw: &Arc<JsonObject>, purpose: &str) -> Result<Arc<JsonObject>, String> {
 match raw.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => {
 let mut object = raw.as_ref().clone();
 object.remove("title");
 object.remove("description");
 Ok(Arc::new(object))
 }
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool {purpose} to have root type 'object', but found '{t}'."
 )),
 None => Err(format!(
 "Schema is missing 'type' field. MCP specification requires {purpose} to have root type 'object'."
 )),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {other:?}. Expected \"object\"."
 )),
 }
}

/// Generate, validate, and strip a JSON schema for inputSchema (must have root type "object";
/// top-level "title" and "description" are removed).
pub fn schema_for_input<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Arc<JsonObject>>> = Default::default();
 static CACHE_FOR_INPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
 };
 CACHE_FOR_INPUT.with(|cache| {
 if let Some(schema) = cache
 if let Some(result) = cache
 .read()
 .expect("input schema cache lock poisoned")
 .get(&TypeId::of::<T>())
 {
 schema.clone()
 } else {
 let mut schema = schema_for_type::<T>().as_ref().clone();

 // Remove unnecessary top-level fields
 schema.remove("title");
 schema.remove("description");

 let schema = Arc::new(schema);
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), schema.clone());

 schema
 return result.clone();
 }
 let result = validate_and_strip(&schema_for_type::<T>(), "inputSchema");
 cache
 .write()
 .expect("input schema cache lock poisoned")
 .insert(TypeId::of::<T>(), result.clone());
 result
 })
}

// TODO: should be updated according to the new specifications
/// Schema used when input is empty.
pub fn schema_for_empty_input() -> Arc<JsonObject> {
 std::sync::Arc::new(
 serde_json::json!({
 "type": "object",
 "properties": {}
 })
 .as_object()
 .unwrap()
 .clone(),
 )
 static EMPTY: LazyLock<Arc<JsonObject>> = LazyLock::new(|| {
 let mut object = JsonObject::new();
 object.insert("type".into(), serde_json::json!("object"));
 object.insert("properties".into(), serde_json::json!({}));
 Arc::new(object)
 });
 EMPTY.clone()
}

/// Generate and validate a JSON schema for outputSchema (must have root type "object").
/// Generate a JSON schema for outputSchema (must have root type "object"; top-level "title" and "description" are removed)
pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObject>, String> {
 thread_local! {
 static CACHE_FOR_OUTPUT: std::sync::RwLock<HashMap<TypeId, Result<Arc<JsonObject>, String>>> = Default::default();
Expand All@@ -108,22 +122,8 @@ pub fn schema_for_output<T: JsonSchema + std::any::Any>() -> Result<Arc<JsonObje
 return result.clone();
 }

 // Generate and validate schema
 let schema = schema_for_type::<T>();
 let result = match schema.get("type") {
 Some(serde_json::Value::String(t)) if t == "object" => Ok(schema.clone()),
 Some(serde_json::Value::String(t)) => Err(format!(
 "MCP specification requires tool outputSchema to have root type 'object', but found '{}'.",
 t
 )),
 None => Err(
 "Schema is missing 'type' field. MCP specification requires outputSchema to have root type 'object'.".to_string()
 ),
 Some(other) => Err(format!(
 "Schema 'type' field has unexpected format: {:?}. Expected \"object\".",
 other
 )),
 };
 // Generate, validate, and strip unnecessary top-level fields
 let result = validate_and_strip(&schema_for_type::<T>(), "outputSchema");

 // Cache the result (both success and error cases)
 cache
Expand DownExpand Up@@ -316,4 +316,40 @@ mod tests {
 let result = schema_for_output::<TestObject>();
 assert!(result.is_ok(),);
 }

 #[test]
 fn test_schema_for_output_strips_top_level_title() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_output_strips_top_level_description() {
 let schema = schema_for_output::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }

 #[test]
 fn test_schema_for_input_rejects_primitive() {
 let result = schema_for_input::<i32>();
 assert!(result.is_err());
 }

 #[test]
 fn test_schema_for_input_accepts_object() {
 let result = schema_for_input::<TestObject>();
 assert!(result.is_ok());
 }

 #[test]
 fn test_schema_for_input_strips_top_level_title() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("title"));
 }

 #[test]
 fn test_schema_for_input_strips_top_level_description() {
 let schema = schema_for_input::<TestObject>().unwrap();
 assert!(!schema.contains_key("description"));
 }
}

11 changes: 9 additions & 2 deletions
crates/rmcp/src/handler/server/router/tool.rs

View file


Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -250,7 +250,9 @@ where
 attr: Tool::new(
 name.into(),
 "",
 schema_for_input::<crate::model::JsonObject>(),
 schema_for_input::<crate::model::JsonObject>().unwrap_or_else(|e| {
 panic!("Invalid input schema for JsonObject: {e}");
 }),
 ),
 call: self,
 _marker: std::marker::PhantomData,
Expand DownExpand Up@@ -287,7 +289,12 @@ where
 self
 }
 pub fn parameters<T: JsonSchema + 'static>(mut self) -> Self {
 self.attr.input_schema = schema_for_input::<T>();
 self.attr.input_schema = schema_for_input::<T>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for `{}`: {e}",
 std::any::type_name::<T>()
 )
 });
 self
 }
 pub fn parameters_value(mut self, schema: serde_json::Value) -> Self {
Expand Down

9 changes: 8 additions & 1 deletion
crates/rmcp/src/handler/server/router/tool/tool_traits.rs

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Open in desktop

Original file line numberDiff line numberDiff line change
Expand Up@@ -49,7 +49,14 @@ pub trait ToolBase {
 /// If the tool does not have any parameters, you should override this methods to return [`None`],
 /// and when invoked, the parameter will get default values.
 fn input_schema() -> Option<Arc<JsonObject>> {
 Some(schema_for_input::<Parameters<Self::Parameter>>())
 Some(
 schema_for_input::<Parameters<Self::Parameter>>().unwrap_or_else(|e| {
 panic!(
 "Invalid input schema for ToolBase::Parameter type `{0}`: {e}",
 std::any::type_name::<Self::Parameter>(),
 );
 }),
 )
 }

 /// Json schema for tool output.
Expand Down

3 changes: 2 additions & 1 deletion
crates/rmcp/src/model/tool.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -330,7 +330,8 @@ impl Tool {
 /// Set the input schema using a type that implements JsonSchema
 #[cfg(feature = "server")]
 pub fn with_input_schema<T: JsonSchema + 'static>(mut self) -> Self {
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>();
 self.input_schema = crate::handler::server::tool::schema_for_input::<T>()
 .unwrap_or_else(|e| panic!("Invalid input schema for tool '{}': {}", self.name, e));
 self
 }

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14 changes: 11 additions & 3 deletions
crates/rmcp/tests/test_list_tools_result.rs

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Original file line numberDiff line numberDiff line change
@@ -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},
};
Expand All@@ -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]
Expand All@@ -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(
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14 changes: 14 additions & 0 deletions
crates/rmcp/tests/test_list_tools_result/list_tools_result.json

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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"
 ]
 }
 }
 ]
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21 changes: 17 additions & 4 deletions
crates/rmcp/tests/test_structured_output.rs

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Original file line numberDiff line numberDiff line change
Expand Up@@ -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 {}

Expand DownExpand Up@@ -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,
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