feat: add local feature for !Send tool handler support (#740)

* feat: add local feature for !Send tool handler support

* fix: gate streamable HTTP transport on not(local) feature

crates/rmcp-macros/Cargo.toml

@@ -22,4 +22,6 @@ serde_json = "1.0"
 darling = { version = "0.23" }
 
 [features]
+local = []
+
 [dev-dependencies]

crates/rmcp-macros/src/tool.rs

@@ -95,6 +95,9 @@ pub struct ToolAttribute {
     pub icons: Option<Expr>,
     /// Optional metadata for the tool
     pub meta: Option<Expr>,
+    /// When true, the generated future will not require `Send`. Useful for `!Send` handlers
+    /// (e.g. single-threaded database connections). Also enabled globally by the `local` crate feature.
+    pub local: bool,
 }
 
 #[derive(FromMeta, Debug, Default)]
@@ -333,7 +336,9 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
     if fn_item.sig.asyncness.is_some() {
         // 1. remove asyncness from sig
         // 2. make return type: `std::pin::Pin<Box<dyn std::future::Future<Output = #ReturnType> + Send + '_>>`
+        //    (omit `+ Send` when the `local` crate feature is active or `#[tool(local)]` is used)
         // 3. make body: { Box::pin(async move { #body }) }
+        let omit_send = cfg!(feature = "local") || attribute.local;
         let new_output = syn::parse2::<ReturnType>({
             let mut lt = quote! { 'static };
             if let Some(receiver) = fn_item.sig.receiver() {
@@ -347,10 +352,18 @@ pub fn tool(attr: TokenStream, input: TokenStream) -> syn::Result<TokenStream> {
             }
             match &fn_item.sig.output {
                 syn::ReturnType::Default => {
-                    quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = ()> + Send + #lt>> }
+                    if omit_send {
+                        quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = ()> + #lt>> }
+                    } else {
+                        quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = ()> + Send + #lt>> }
+                    }
                 }
                 syn::ReturnType::Type(_, ty) => {
-                    quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = #ty> + Send + #lt>> }
+                    if omit_send {
+                        quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = #ty> + #lt>> }
+                    } else {
+                        quote! { -> ::std::pin::Pin<Box<dyn ::std::future::Future<Output = #ty> + Send + #lt>> }
+                    }
                 }
             }
         })?;

crates/rmcp/Cargo.toml

@@ -77,6 +77,7 @@ chrono = { version = "0.4.38", default-features = false, features = [
 
 [features]
 default = ["base64", "macros", "server"]
+local = ["rmcp-macros?/local"]
 client = ["dep:tokio-stream"]
 server = ["transport-async-rw", "dep:schemars", "dep:pastey"]
 macros = ["dep:rmcp-macros", "dep:pastey"]

crates/rmcp/README.md

@@ -52,7 +52,7 @@ The transport layer is pluggable. Two built-in pairs cover the most common cases
 | | Client | Server |
 |:-:|:-:|:-:|
 | **stdio** | [`TokioChildProcess`](crate::transport::TokioChildProcess) | [`stdio`](crate::transport::stdio) |
-| **Streamable HTTP** | [`StreamableHttpClientTransport`](crate::transport::StreamableHttpClientTransport) | [`StreamableHttpService`](crate::transport::StreamableHttpService) |
+| **Streamable HTTP** | [`StreamableHttpClientTransport`](crate::transport::StreamableHttpClientTransport) | `StreamableHttpService` |
 
 Any type that implements the [`Transport`](crate::transport::Transport) trait can be used. The [`IntoTransport`](crate::transport::IntoTransport) helper trait provides automatic conversions from:
 

crates/rmcp/src/handler/client.rs

@@ -4,7 +4,9 @@ use std::sync::Arc;
 use crate::{
     error::ErrorData as McpError,
     model::*,
-    service::{NotificationContext, RequestContext, RoleClient, Service, ServiceRole},
+    service::{
+        MaybeSendFuture, NotificationContext, RequestContext, RoleClient, Service, ServiceRole,
+    },
 };
 
 impl<H: ClientHandler> Service<RoleClient> for H {
@@ -83,7 +85,7 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
     fn ping(
         &self,
         context: RequestContext<RoleClient>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(()))
     }
 
@@ -91,7 +93,7 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
         &self,
         params: CreateMessageRequestParams,
         context: RequestContext<RoleClient>,
-    ) -> impl Future<Output = Result<CreateMessageResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CreateMessageResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(
             McpError::method_not_found::<CreateMessageRequestMethod>(),
         ))
@@ -100,7 +102,7 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
     fn list_roots(
         &self,
         context: RequestContext<RoleClient>,
-    ) -> impl Future<Output = Result<ListRootsResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListRootsResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(ListRootsResult::default()))
     }
 
@@ -162,7 +164,8 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
         &self,
         request: CreateElicitationRequestParams,
         context: RequestContext<RoleClient>,
-    ) -> impl Future<Output = Result<CreateElicitationResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CreateElicitationResult, McpError>> + MaybeSendFuture + '_
+    {
         // Default implementation declines all requests - real clients should override this
         let _ = (request, context);
         std::future::ready(Ok(CreateElicitationResult {
@@ -175,7 +178,7 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
         &self,
         request: CustomRequest,
         context: RequestContext<RoleClient>,
-    ) -> impl Future<Output = Result<CustomResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CustomResult, McpError>> + MaybeSendFuture + '_ {
         let CustomRequest { method, .. } = request;
         let _ = context;
         std::future::ready(Err(McpError::new(
@@ -189,46 +192,46 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
         &self,
         params: CancelledNotificationParam,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_progress(
         &self,
         params: ProgressNotificationParam,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_logging_message(
         &self,
         params: LoggingMessageNotificationParam,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_resource_updated(
         &self,
         params: ResourceUpdatedNotificationParam,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_resource_list_changed(
         &self,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_tool_list_changed(
         &self,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_prompt_list_changed(
         &self,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
 
@@ -236,14 +239,14 @@ pub trait ClientHandler: Sized + Send + Sync + 'static {
         &self,
         params: ElicitationResponseNotificationParam,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_custom_notification(
         &self,
         notification: CustomNotification,
         context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         let _ = (notification, context);
         std::future::ready(())
     }
@@ -269,7 +272,7 @@ macro_rules! impl_client_handler_for_wrapper {
             fn ping(
                 &self,
                 context: RequestContext<RoleClient>,
-            ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
                 (**self).ping(context)
             }
 
@@ -277,14 +280,14 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 params: CreateMessageRequestParams,
                 context: RequestContext<RoleClient>,
-            ) -> impl Future<Output = Result<CreateMessageResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CreateMessageResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).create_message(params, context)
             }
 
             fn list_roots(
                 &self,
                 context: RequestContext<RoleClient>,
-            ) -> impl Future<Output = Result<ListRootsResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ListRootsResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).list_roots(context)
             }
 
@@ -292,7 +295,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 request: CreateElicitationRequestParams,
                 context: RequestContext<RoleClient>,
-            ) -> impl Future<Output = Result<CreateElicitationResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CreateElicitationResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).create_elicitation(request, context)
             }
 
@@ -300,7 +303,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 request: CustomRequest,
                 context: RequestContext<RoleClient>,
-            ) -> impl Future<Output = Result<CustomResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CustomResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).on_custom_request(request, context)
             }
 
@@ -308,7 +311,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 params: CancelledNotificationParam,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_cancelled(params, context)
             }
 
@@ -316,7 +319,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 params: ProgressNotificationParam,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_progress(params, context)
             }
 
@@ -324,7 +327,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 params: LoggingMessageNotificationParam,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_logging_message(params, context)
             }
 
@@ -332,28 +335,28 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 params: ResourceUpdatedNotificationParam,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_resource_updated(params, context)
             }
 
             fn on_resource_list_changed(
                 &self,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_resource_list_changed(context)
             }
 
             fn on_tool_list_changed(
                 &self,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_tool_list_changed(context)
             }
 
             fn on_prompt_list_changed(
                 &self,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_prompt_list_changed(context)
             }
 
@@ -361,7 +364,7 @@ macro_rules! impl_client_handler_for_wrapper {
                 &self,
                 notification: CustomNotification,
                 context: NotificationContext<RoleClient>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_custom_notification(notification, context)
             }
 

crates/rmcp/src/handler/server.rs

@@ -3,7 +3,10 @@ use std::sync::Arc;
 use crate::{
     error::ErrorData as McpError,
     model::{TaskSupport, *},
-    service::{NotificationContext, RequestContext, RoleServer, Service, ServiceRole},
+    service::{
+        MaybeSend, MaybeSendFuture, NotificationContext, RequestContext, RoleServer, Service,
+        ServiceRole,
+    },
 };
 
 pub mod common;
@@ -159,12 +162,16 @@ impl<H: ServerHandler> Service<RoleServer> for H {
 }
 
 #[allow(unused_variables)]
-pub trait ServerHandler: Sized + Send + Sync + 'static {
+#[allow(
+    private_bounds,
+    reason = "MaybeSend is a sealed conditional Send + Sync alias"
+)]
+pub trait ServerHandler: Sized + MaybeSend + 'static {
     fn enqueue_task(
         &self,
         _request: CallToolRequestParams,
         _context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<CreateTaskResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CreateTaskResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::internal_error(
             "Task processing not implemented".to_string(),
             None,
@@ -173,7 +180,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
     fn ping(
         &self,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(()))
     }
     // handle requests
@@ -181,7 +188,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: InitializeRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<InitializeResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<InitializeResult, McpError>> + MaybeSendFuture + '_ {
         if context.peer.peer_info().is_none() {
             context.peer.set_peer_info(request);
         }
@@ -191,49 +198,50 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: CompleteRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<CompleteResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CompleteResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(CompleteResult::default()))
     }
     fn set_level(
         &self,
         request: SetLevelRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<SetLevelRequestMethod>()))
     }
     fn get_prompt(
         &self,
         request: GetPromptRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<GetPromptResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<GetPromptResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<GetPromptRequestMethod>()))
     }
     fn list_prompts(
         &self,
         request: Option<PaginatedRequestParams>,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListPromptsResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListPromptsResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(ListPromptsResult::default()))
     }
     fn list_resources(
         &self,
         request: Option<PaginatedRequestParams>,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListResourcesResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListResourcesResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(ListResourcesResult::default()))
     }
     fn list_resource_templates(
         &self,
         request: Option<PaginatedRequestParams>,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>> + MaybeSendFuture + '_
+    {
         std::future::ready(Ok(ListResourceTemplatesResult::default()))
     }
     fn read_resource(
         &self,
         request: ReadResourceRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(
             McpError::method_not_found::<ReadResourceRequestMethod>(),
         ))
@@ -242,28 +250,28 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: SubscribeRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<SubscribeRequestMethod>()))
     }
     fn unsubscribe(
         &self,
         request: UnsubscribeRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<UnsubscribeRequestMethod>()))
     }
     fn call_tool(
         &self,
         request: CallToolRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<CallToolResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CallToolResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<CallToolRequestMethod>()))
     }
     fn list_tools(
         &self,
         request: Option<PaginatedRequestParams>,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListToolsResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListToolsResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(ListToolsResult::default()))
     }
     /// Get a tool definition by name.
@@ -277,7 +285,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: CustomRequest,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<CustomResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CustomResult, McpError>> + MaybeSendFuture + '_ {
         let CustomRequest { method, .. } = request;
         let _ = context;
         std::future::ready(Err(McpError::new(
@@ -291,34 +299,34 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         notification: CancelledNotificationParam,
         context: NotificationContext<RoleServer>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_progress(
         &self,
         notification: ProgressNotificationParam,
         context: NotificationContext<RoleServer>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_initialized(
         &self,
         context: NotificationContext<RoleServer>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         tracing::info!("client initialized");
         std::future::ready(())
     }
     fn on_roots_list_changed(
         &self,
         context: NotificationContext<RoleServer>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         std::future::ready(())
     }
     fn on_custom_notification(
         &self,
         notification: CustomNotification,
         context: NotificationContext<RoleServer>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         let _ = (notification, context);
         std::future::ready(())
     }
@@ -331,7 +339,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: Option<PaginatedRequestParams>,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<ListTasksResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<ListTasksResult, McpError>> + MaybeSendFuture + '_ {
         std::future::ready(Err(McpError::method_not_found::<ListTasksMethod>()))
     }
 
@@ -339,7 +347,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: GetTaskInfoParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<GetTaskResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<GetTaskResult, McpError>> + MaybeSendFuture + '_ {
         let _ = (request, context);
         std::future::ready(Err(McpError::method_not_found::<GetTaskInfoMethod>()))
     }
@@ -348,7 +356,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: GetTaskResultParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<GetTaskPayloadResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<GetTaskPayloadResult, McpError>> + MaybeSendFuture + '_ {
         let _ = (request, context);
         std::future::ready(Err(McpError::method_not_found::<GetTaskResultMethod>()))
     }
@@ -357,7 +365,7 @@ pub trait ServerHandler: Sized + Send + Sync + 'static {
         &self,
         request: CancelTaskParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<CancelTaskResult, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<CancelTaskResult, McpError>> + MaybeSendFuture + '_ {
         let _ = (request, context);
         std::future::ready(Err(McpError::method_not_found::<CancelTaskMethod>()))
     }
@@ -370,14 +378,14 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CallToolRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CreateTaskResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CreateTaskResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).enqueue_task(request, context)
             }
 
             fn ping(
                 &self,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
                 (**self).ping(context)
             }
 
@@ -385,7 +393,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: InitializeRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<InitializeResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<InitializeResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).initialize(request, context)
             }
 
@@ -393,7 +401,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CompleteRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CompleteResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CompleteResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).complete(request, context)
             }
 
@@ -401,7 +409,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: SetLevelRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
                 (**self).set_level(request, context)
             }
 
@@ -409,7 +417,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: GetPromptRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<GetPromptResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<GetPromptResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).get_prompt(request, context)
             }
 
@@ -417,7 +425,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: Option<PaginatedRequestParams>,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ListPromptsResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ListPromptsResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).list_prompts(request, context)
             }
 
@@ -425,7 +433,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: Option<PaginatedRequestParams>,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ListResourcesResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ListResourcesResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).list_resources(request, context)
             }
 
@@ -433,7 +441,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: Option<PaginatedRequestParams>,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>> + Send + '_
+            ) -> impl Future<Output = Result<ListResourceTemplatesResult, McpError>> + MaybeSendFuture + '_
             {
                 (**self).list_resource_templates(request, context)
             }
@@ -442,7 +450,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: ReadResourceRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ReadResourceResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).read_resource(request, context)
             }
 
@@ -450,7 +458,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: SubscribeRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
                 (**self).subscribe(request, context)
             }
 
@@ -458,7 +466,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: UnsubscribeRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
                 (**self).unsubscribe(request, context)
             }
 
@@ -466,7 +474,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CallToolRequestParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CallToolResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CallToolResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).call_tool(request, context)
             }
 
@@ -474,7 +482,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: Option<PaginatedRequestParams>,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ListToolsResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ListToolsResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).list_tools(request, context)
             }
 
@@ -486,7 +494,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CustomRequest,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CustomResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CustomResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).on_custom_request(request, context)
             }
 
@@ -494,7 +502,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 notification: CancelledNotificationParam,
                 context: NotificationContext<RoleServer>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_cancelled(notification, context)
             }
 
@@ -502,21 +510,21 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 notification: ProgressNotificationParam,
                 context: NotificationContext<RoleServer>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_progress(notification, context)
             }
 
             fn on_initialized(
                 &self,
                 context: NotificationContext<RoleServer>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_initialized(context)
             }
 
             fn on_roots_list_changed(
                 &self,
                 context: NotificationContext<RoleServer>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_roots_list_changed(context)
             }
 
@@ -524,7 +532,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 notification: CustomNotification,
                 context: NotificationContext<RoleServer>,
-            ) -> impl Future<Output = ()> + Send + '_ {
+            ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
                 (**self).on_custom_notification(notification, context)
             }
 
@@ -536,7 +544,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: Option<PaginatedRequestParams>,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<ListTasksResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<ListTasksResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).list_tasks(request, context)
             }
 
@@ -544,7 +552,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: GetTaskInfoParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<GetTaskResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<GetTaskResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).get_task_info(request, context)
             }
 
@@ -552,7 +560,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: GetTaskResultParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<GetTaskPayloadResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<GetTaskPayloadResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).get_task_result(request, context)
             }
 
@@ -560,7 +568,7 @@ macro_rules! impl_server_handler_for_wrapper {
                 &self,
                 request: CancelTaskParams,
                 context: RequestContext<RoleServer>,
-            ) -> impl Future<Output = Result<CancelTaskResult, McpError>> + Send + '_ {
+            ) -> impl Future<Output = Result<CancelTaskResult, McpError>> + MaybeSendFuture + '_ {
                 (**self).cancel_task(request, context)
             }
         }

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

@@ -6,7 +6,8 @@
 
 use std::{future::Future, marker::PhantomData};
 
-use futures::future::{BoxFuture, FutureExt};
+#[cfg(not(feature = "local"))]
+use futures::future::BoxFuture;
 use serde::de::DeserializeOwned;
 
 use super::common::{AsRequestContext, FromContextPart};
@@ -15,7 +16,7 @@ use crate::{
     RoleServer,
     handler::server::wrapper::Parameters,
     model::{GetPromptResult, PromptMessage},
-    service::RequestContext,
+    service::{MaybeBoxFuture, MaybeSend, MaybeSendFuture, RequestContext},
 };
 
 /// Context for prompt retrieval operations
@@ -57,14 +58,23 @@ pub trait GetPromptHandler<S, A> {
     fn handle(
         self,
         context: PromptContext<'_, S>,
-    ) -> BoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>;
+    ) -> MaybeBoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>;
 }
 
 /// Type alias for dynamic prompt handlers
+#[cfg(not(feature = "local"))]
 pub type DynGetPromptHandler<S> = dyn for<'a> Fn(PromptContext<'a, S>) -> BoxFuture<'a, Result<GetPromptResult, crate::ErrorData>>
     + Send
     + Sync;
 
+#[cfg(feature = "local")]
+pub type DynGetPromptHandler<S> = dyn for<'a> Fn(
+    PromptContext<'a, S>,
+) -> futures::future::LocalBoxFuture<
+    'a,
+    Result<GetPromptResult, crate::ErrorData>,
+>;
+
 /// Adapter type for async methods that return `Vec<PromptMessage>`
 pub struct AsyncMethodAdapter<T>(PhantomData<T>);
 
@@ -191,31 +201,31 @@ macro_rules! impl_prompt_handler_for {
         impl<$($Tn,)* S, F, R> GetPromptHandler<S, ($($Tn,)*)> for F
         where
             $(
-                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + Send,
+                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + MaybeSendFuture,
             )*
-            F: FnOnce(&S, $($Tn,)*) -> BoxFuture<'_, R> + Send,
+            F: FnOnce(&S, $($Tn,)*) -> MaybeBoxFuture<'_, R> + MaybeSendFuture,
-            R: IntoGetPromptResult + Send + 'static,
+            R: IntoGetPromptResult + MaybeSendFuture + 'static,
-            S: Send + Sync + 'static,
+            S: MaybeSend + 'static,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn handle(
                 self,
                 mut context: PromptContext<'_, S>,
-            ) -> BoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
             {
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
                 let service = context.server;
                 let fut = self(service, $($Tn,)*);
-                async move {
+                Box::pin(async move {
                     let result = fut.await;
                     result.into_get_prompt_result()
-                }.boxed()
+                })
             }
         }
 
@@ -224,28 +234,28 @@ macro_rules! impl_prompt_handler_for {
         impl<$($Tn,)* S, F, R> GetPromptHandler<S, SyncPromptMethodAdapter<($($Tn,)*), R>> for F
         where
             $(
-                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + Send,
+                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + MaybeSendFuture,
             )*
-            F: FnOnce(&S, $($Tn,)*) -> R + Send,
+            F: FnOnce(&S, $($Tn,)*) -> R + MaybeSendFuture,
-            R: IntoGetPromptResult + Send,
+            R: IntoGetPromptResult + MaybeSendFuture,
-            S: Send + Sync,
+            S: MaybeSend,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn handle(
                 self,
                 mut context: PromptContext<'_, S>,
-            ) -> BoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
             {
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
                 let service = context.server;
                 let result = self(service, $($Tn,)*);
-                std::future::ready(result.into_get_prompt_result()).boxed()
+                Box::pin(std::future::ready(result.into_get_prompt_result()))
             }
         }
 
@@ -254,25 +264,25 @@ macro_rules! impl_prompt_handler_for {
         impl<$($Tn,)* S, F, Fut, R> GetPromptHandler<S, AsyncPromptAdapter<($($Tn,)*), Fut, R>> for F
         where
             $(
-                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + Send + 'static,
+                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + MaybeSendFuture + 'static,
             )*
-            F: FnOnce($($Tn,)*) -> Fut + Send + 'static,
+            F: FnOnce($($Tn,)*) -> Fut + MaybeSendFuture + 'static,
-            Fut: Future<Output = Result<R, crate::ErrorData>> + Send + 'static,
+            Fut: Future<Output = Result<R, crate::ErrorData>> + MaybeSendFuture + 'static,
-            R: IntoGetPromptResult + Send + 'static,
+            R: IntoGetPromptResult + MaybeSendFuture + 'static,
-            S: Send + Sync + 'static,
+            S: MaybeSend + 'static,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn handle(
                 self,
                 mut context: PromptContext<'_, S>,
-            ) -> BoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
             {
                 // Extract all parameters before moving into the async block
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
 
@@ -290,27 +300,27 @@ macro_rules! impl_prompt_handler_for {
         impl<$($Tn,)* S, F, R> GetPromptHandler<S, SyncPromptAdapter<($($Tn,)*), R>> for F
         where
             $(
-                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + Send + 'static,
+                $Tn: for<'a> FromContextPart<PromptContext<'a, S>> + MaybeSendFuture + 'static,
             )*
-            F: FnOnce($($Tn,)*) -> Result<R, crate::ErrorData> + Send + 'static,
+            F: FnOnce($($Tn,)*) -> Result<R, crate::ErrorData> + MaybeSendFuture + 'static,
-            R: IntoGetPromptResult + Send + 'static,
+            R: IntoGetPromptResult + MaybeSendFuture + 'static,
-            S: Send + Sync,
+            S: MaybeSend,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn handle(
                 self,
                 mut context: PromptContext<'_, S>,
-            ) -> BoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'_, Result<GetPromptResult, crate::ErrorData>>
             {
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
                 let result = self($($Tn,)*);
-                std::future::ready(result.and_then(|r| r.into_get_prompt_result())).boxed()
+                Box::pin(std::future::ready(result.and_then(|r| r.into_get_prompt_result())))
             }
         }
 

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

@@ -1,10 +1,9 @@
 use std::{borrow::Cow, sync::Arc};
 
-use futures::future::BoxFuture;
-
 use crate::{
     handler::server::prompt::{DynGetPromptHandler, GetPromptHandler, PromptContext},
     model::{GetPromptResult, Prompt},
+    service::{MaybeBoxFuture, MaybeSend},
 };
 
 pub struct PromptRoute<S> {
@@ -32,10 +31,10 @@ impl<S> Clone for PromptRoute<S> {
     }
 }
 
-impl<S: Send + Sync + 'static> PromptRoute<S> {
+impl<S: MaybeSend + 'static> PromptRoute<S> {
     pub fn new<H, A: 'static>(attr: impl Into<Prompt>, handler: H) -> Self
     where
-        H: GetPromptHandler<S, A> + Send + Sync + Clone + 'static,
+        H: GetPromptHandler<S, A> + MaybeSend + Clone + 'static,
     {
         Self {
             get: Arc::new(move |context: PromptContext<S>| {
@@ -50,9 +49,8 @@ impl<S: Send + Sync + 'static> PromptRoute<S> {
     where
         H: for<'a> Fn(
                 PromptContext<'a, S>,
-            ) -> BoxFuture<'a, Result<GetPromptResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'a, Result<GetPromptResult, crate::ErrorData>>
-            + Send
+            + MaybeSend
-            + Sync
             + 'static,
     {
         Self {
@@ -72,9 +70,9 @@ pub trait IntoPromptRoute<S, A> {
 
 impl<S, H, A, P> IntoPromptRoute<S, A> for (P, H)
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
     A: 'static,
-    H: GetPromptHandler<S, A> + Send + Sync + Clone + 'static,
+    H: GetPromptHandler<S, A> + MaybeSend + Clone + 'static,
     P: Into<Prompt>,
 {
     fn into_prompt_route(self) -> PromptRoute<S> {
@@ -84,7 +82,7 @@ where
 
 impl<S> IntoPromptRoute<S, ()> for PromptRoute<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     fn into_prompt_route(self) -> PromptRoute<S> {
         self
@@ -96,7 +94,7 @@ pub struct PromptAttrGenerateFunctionAdapter;
 
 impl<S, F> IntoPromptRoute<S, PromptAttrGenerateFunctionAdapter> for F
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
     F: Fn() -> PromptRoute<S>,
 {
     fn into_prompt_route(self) -> PromptRoute<S> {
@@ -137,7 +135,7 @@ impl<S> IntoIterator for PromptRouter<S> {
 
 impl<S> PromptRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     pub fn new() -> Self {
         Self {
@@ -195,7 +193,7 @@ where
 
 impl<S> std::ops::Add<PromptRouter<S>> for PromptRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     type Output = Self;
 
@@ -207,7 +205,7 @@ where
 
 impl<S> std::ops::AddAssign<PromptRouter<S>> for PromptRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     fn add_assign(&mut self, other: PromptRouter<S>) {
         self.merge(other);

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

@@ -124,7 +124,6 @@ mod tool_traits;
 
 use std::{borrow::Cow, sync::Arc};
 
-use futures::{FutureExt, future::BoxFuture};
 use schemars::JsonSchema;
 pub use tool_traits::{AsyncTool, SyncTool, ToolBase};
 
@@ -134,6 +133,7 @@ use crate::{
         tool_name_validation::validate_and_warn_tool_name,
     },
     model::{CallToolResult, Tool, ToolAnnotations},
+    service::{MaybeBoxFuture, MaybeSend},
 };
 
 pub struct ToolRoute<S> {
@@ -161,15 +161,15 @@ impl<S> Clone for ToolRoute<S> {
     }
 }
 
-impl<S: Send + Sync + 'static> ToolRoute<S> {
+impl<S: MaybeSend + 'static> ToolRoute<S> {
     pub fn new<C, A>(attr: impl Into<Tool>, call: C) -> Self
     where
-        C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+        C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
     {
         Self {
             call: Arc::new(move |context: ToolCallContext<S>| {
                 let call = call.clone();
-                context.invoke(call).boxed()
+                context.invoke(call)
             }),
             attr: attr.into(),
         }
@@ -178,9 +178,8 @@ impl<S: Send + Sync + 'static> ToolRoute<S> {
     where
         C: for<'a> Fn(
                 ToolCallContext<'a, S>,
-            ) -> BoxFuture<'a, Result<CallToolResult, crate::ErrorData>>
+            ) -> MaybeBoxFuture<'a, Result<CallToolResult, crate::ErrorData>>
-            + Send
+            + MaybeSend
-            + Sync
             + 'static,
     {
         Self {
@@ -199,8 +198,8 @@ pub trait IntoToolRoute<S, A> {
 
 impl<S, C, A, T> IntoToolRoute<S, A> for (T, C)
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
-    C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
     T: Into<Tool>,
 {
     fn into_tool_route(self) -> ToolRoute<S> {
@@ -210,7 +209,7 @@ where
 
 impl<S> IntoToolRoute<S, ()> for ToolRoute<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     fn into_tool_route(self) -> ToolRoute<S> {
         self
@@ -220,7 +219,7 @@ where
 pub struct ToolAttrGenerateFunctionAdapter;
 impl<S, F> IntoToolRoute<S, ToolAttrGenerateFunctionAdapter> for F
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
     F: Fn() -> ToolRoute<S>,
 {
     fn into_tool_route(self) -> ToolRoute<S> {
@@ -230,14 +229,14 @@ where
 
 pub trait CallToolHandlerExt<S, A>: Sized
 where
-    Self: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    Self: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
 {
     fn name(self, name: impl Into<Cow<'static, str>>) -> WithToolAttr<Self, S, A>;
 }
 
 impl<C, S, A> CallToolHandlerExt<S, A> for C
 where
-    C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
 {
     fn name(self, name: impl Into<Cow<'static, str>>) -> WithToolAttr<Self, S, A> {
         WithToolAttr {
@@ -254,7 +253,7 @@ where
 
 pub struct WithToolAttr<C, S, A>
 where
-    C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
 {
     pub attr: crate::model::Tool,
     pub call: C,
@@ -263,8 +262,8 @@ where
 
 impl<C, S, A> IntoToolRoute<S, A> for WithToolAttr<C, S, A>
 where
-    C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     fn into_tool_route(self) -> ToolRoute<S> {
         ToolRoute::new(self.attr, self.call)
@@ -273,7 +272,7 @@ where
 
 impl<C, S, A> WithToolAttr<C, S, A>
 where
-    C: CallToolHandler<S, A> + Send + Sync + Clone + 'static,
+    C: CallToolHandler<S, A> + MaybeSend + Clone + 'static,
 {
     pub fn description(mut self, description: impl Into<Cow<'static, str>>) -> Self {
         self.attr.description = Some(description.into());
@@ -328,7 +327,7 @@ impl<S> IntoIterator for ToolRouter<S> {
 
 impl<S> ToolRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     pub fn new() -> Self {
         Self {
@@ -428,7 +427,7 @@ where
 
 impl<S> std::ops::Add<ToolRouter<S>> for ToolRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     type Output = Self;
 
@@ -440,7 +439,7 @@ where
 
 impl<S> std::ops::AddAssign<ToolRouter<S>> for ToolRouter<S>
 where
-    S: Send + Sync + 'static,
+    S: MaybeSend + 'static,
 {
     fn add_assign(&mut self, other: ToolRouter<S>) {
         self.merge(other);

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

@@ -1,4 +1,4 @@
-use std::{borrow::Cow, pin::Pin, sync::Arc};
+use std::{borrow::Cow, future::Future, sync::Arc};
 
 use serde::{Deserialize, Serialize};
 
@@ -11,6 +11,7 @@ use crate::{
     },
     model::{Icon, JsonObject, Meta, ToolAnnotations, ToolExecution},
     schemars::JsonSchema,
+    service::{MaybeSend, MaybeSendFuture},
 };
 
 /// Base trait to define attributes of a tool.
@@ -84,7 +85,8 @@ pub trait ToolBase {
 ///
 /// Consider using [`AsyncTool`] if your workflow involves asynchronous operations.
 /// Examples are shown in [the module-level documentation][crate::handler::server::router::tool].
-pub trait SyncTool<S: Sync + Send + 'static>: ToolBase {
+#[allow(private_bounds)]
+pub trait SyncTool<S: MaybeSend + 'static>: ToolBase {
     fn invoke(service: &S, param: Self::Parameter) -> Result<Self::Output, Self::Error>;
 }
 
@@ -92,11 +94,12 @@ pub trait SyncTool<S: Sync + Send + 'static>: ToolBase {
 ///
 /// Consider using [`SyncTool`] if your workflow does not involve asynchronous operations.
 /// Examples are shown in [the module-level documentation][crate::handler::server::router::tool].
-pub trait AsyncTool<S: Sync + Send + 'static>: ToolBase {
+#[allow(private_bounds)]
+pub trait AsyncTool<S: MaybeSend + 'static>: ToolBase {
     fn invoke(
         service: &S,
         param: Self::Parameter,
-    ) -> impl Future<Output = Result<Self::Output, Self::Error>> + Send;
+    ) -> impl Future<Output = Result<Self::Output, Self::Error>> + MaybeSendFuture;
 }
 
 pub(crate) fn tool_attribute<T: ToolBase>() -> crate::model::Tool {
@@ -113,14 +116,14 @@ pub(crate) fn tool_attribute<T: ToolBase>() -> crate::model::Tool {
     }
 }
 
-pub(crate) fn sync_tool_wrapper<S: Sync + Send + 'static, T: SyncTool<S>>(
+pub(crate) fn sync_tool_wrapper<S: MaybeSend + 'static, T: SyncTool<S>>(
     service: &S,
     Parameters(params): Parameters<T::Parameter>,
 ) -> Result<Json<T::Output>, ErrorData> {
     T::invoke(service, params).map(Json).map_err(Into::into)
 }
 
-pub(crate) fn sync_tool_wrapper_with_empty_params<S: Sync + Send + 'static, T: SyncTool<S>>(
+pub(crate) fn sync_tool_wrapper_with_empty_params<S: MaybeSend + 'static, T: SyncTool<S>>(
     service: &S,
 ) -> Result<Json<T::Output>, ErrorData> {
     T::invoke(service, T::Parameter::default())
@@ -128,11 +131,10 @@ pub(crate) fn sync_tool_wrapper_with_empty_params<S: Sync + Send + 'static, T: S
         .map_err(Into::into)
 }
 
-#[expect(clippy::type_complexity)]
+pub(crate) fn async_tool_wrapper<S: MaybeSend + 'static, T: AsyncTool<S>>(
-pub(crate) fn async_tool_wrapper<S: Sync + Send + 'static, T: AsyncTool<S>>(
     service: &S,
     Parameters(params): Parameters<T::Parameter>,
-) -> Pin<Box<dyn Future<Output = Result<Json<T::Output>, ErrorData>> + Send + '_>> {
+) -> crate::service::MaybeBoxFuture<'_, Result<Json<T::Output>, ErrorData>> {
     Box::pin(async move {
         T::invoke(service, params)
             .await
@@ -141,10 +143,9 @@ pub(crate) fn async_tool_wrapper<S: Sync + Send + 'static, T: AsyncTool<S>>(
     })
 }
 
-#[expect(clippy::type_complexity)]
+pub(crate) fn async_tool_wrapper_with_empty_params<S: MaybeSend + 'static, T: AsyncTool<S>>(
-pub(crate) fn async_tool_wrapper_with_empty_params<S: Sync + Send + 'static, T: AsyncTool<S>>(
     service: &S,
-) -> Pin<Box<dyn Future<Output = Result<Json<T::Output>, ErrorData>> + Send + '_>> {
+) -> crate::service::MaybeBoxFuture<'_, Result<Json<T::Output>, ErrorData>> {
     Box::pin(async move {
         T::invoke(service, T::Parameter::default())
             .await

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

@@ -4,7 +4,8 @@ use std::{
     marker::PhantomData,
 };
 
-use futures::future::{BoxFuture, FutureExt};
+#[cfg(not(feature = "local"))]
+use futures::future::BoxFuture;
 use serde::de::DeserializeOwned;
 
 use super::common::{AsRequestContext, FromContextPart};
@@ -16,7 +17,7 @@ use crate::{
     RoleServer,
     handler::server::wrapper::Parameters,
     model::{CallToolRequestParams, CallToolResult, IntoContents, JsonObject},
-    service::RequestContext,
+    service::{MaybeBoxFuture, MaybeSend, MaybeSendFuture, RequestContext},
 };
 
 /// Deserialize a JSON object into a type
@@ -146,13 +147,21 @@ pub trait CallToolHandler<S, A> {
     fn call(
         self,
         context: ToolCallContext<'_, S>,
-    ) -> BoxFuture<'_, Result<CallToolResult, crate::ErrorData>>;
+    ) -> MaybeBoxFuture<'_, Result<CallToolResult, crate::ErrorData>>;
 }
 
+#[cfg(not(feature = "local"))]
 pub type DynCallToolHandler<S> = dyn for<'s> Fn(ToolCallContext<'s, S>) -> BoxFuture<'s, Result<CallToolResult, crate::ErrorData>>
     + Send
     + Sync;
 
+#[cfg(feature = "local")]
+pub type DynCallToolHandler<S> =
+    dyn for<'s> Fn(
+        ToolCallContext<'s, S>,
+    )
+        -> futures::future::LocalBoxFuture<'s, Result<CallToolResult, crate::ErrorData>>;
+
 // Tool-specific extractor for tool name
 pub struct ToolName(pub Cow<'static, str>);
 
@@ -189,7 +198,7 @@ impl<S> FromContextPart<ToolCallContext<'_, S>> for JsonObject {
 }
 
 impl<'s, S> ToolCallContext<'s, S> {
-    pub fn invoke<H, A>(self, h: H) -> BoxFuture<'s, Result<CallToolResult, crate::ErrorData>>
+    pub fn invoke<H, A>(self, h: H) -> MaybeBoxFuture<'s, Result<CallToolResult, crate::ErrorData>>
     where
         H: CallToolHandler<S, A>,
     {
@@ -221,31 +230,31 @@ macro_rules! impl_for {
             $(
                 $Tn: for<'a> FromContextPart<ToolCallContext<'a, S>> ,
             )*
-            F: FnOnce(&S, $($Tn,)*) -> BoxFuture<'_, R>,
+            F: FnOnce(&S, $($Tn,)*) -> MaybeBoxFuture<'_, R>,
 
             // Need RTN support here(I guess), https://github.com/rust-lang/rust/pull/138424
             // Fut: Future<Output = R> + Send + 'a,
-            R: IntoCallToolResult + Send + 'static,
+            R: IntoCallToolResult + MaybeSendFuture + 'static,
-            S: Send + Sync + 'static,
+            S: MaybeSend + 'static,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn call(
                 self,
                 mut context: ToolCallContext<'_, S>,
-            ) -> BoxFuture<'_, Result<CallToolResult, crate::ErrorData>>{
+            ) -> MaybeBoxFuture<'_, Result<CallToolResult, crate::ErrorData>>{
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
                 let service = context.service;
                 let fut = self(service, $($Tn,)*);
-                async move {
+                Box::pin(async move {
                     let result = fut.await;
                     result.into_call_tool_result()
-                }.boxed()
+                })
             }
         }
 
@@ -254,28 +263,28 @@ macro_rules! impl_for {
             $(
                 $Tn: for<'a> FromContextPart<ToolCallContext<'a, S>> ,
             )*
-            F: FnOnce($($Tn,)*) -> Fut + Send + ,
+            F: FnOnce($($Tn,)*) -> Fut + MaybeSendFuture,
-            Fut: Future<Output = R> + Send + 'static,
+            Fut: Future<Output = R> + MaybeSendFuture + 'static,
-            R: IntoCallToolResult + Send + 'static,
+            R: IntoCallToolResult + MaybeSendFuture + 'static,
-            S: Send + Sync,
+            S: MaybeSend,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn call(
                 self,
                 mut context: ToolCallContext<S>,
-            ) -> BoxFuture<'static, Result<CallToolResult, crate::ErrorData>>{
+            ) -> MaybeBoxFuture<'static, Result<CallToolResult, crate::ErrorData>>{
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
                 let fut = self($($Tn,)*);
-                async move {
+                Box::pin(async move {
                     let result = fut.await;
                     result.into_call_tool_result()
-                }.boxed()
+                })
             }
         }
 
@@ -284,23 +293,23 @@ macro_rules! impl_for {
             $(
                 $Tn: for<'a> FromContextPart<ToolCallContext<'a, S>> + ,
             )*
-            F: FnOnce(&S, $($Tn,)*) -> R + Send + ,
+            F: FnOnce(&S, $($Tn,)*) -> R + MaybeSendFuture,
-            R: IntoCallToolResult + Send + ,
+            R: IntoCallToolResult + MaybeSendFuture,
-            S: Send + Sync,
+            S: MaybeSend,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn call(
                 self,
                 mut context: ToolCallContext<S>,
-            ) -> BoxFuture<'static, Result<CallToolResult, crate::ErrorData>> {
+            ) -> MaybeBoxFuture<'static, Result<CallToolResult, crate::ErrorData>> {
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
-                std::future::ready(self(context.service, $($Tn,)*).into_call_tool_result()).boxed()
+                Box::pin(std::future::ready(self(context.service, $($Tn,)*).into_call_tool_result()))
             }
         }
 
@@ -309,23 +318,23 @@ macro_rules! impl_for {
             $(
                 $Tn: for<'a> FromContextPart<ToolCallContext<'a, S>> + ,
             )*
-            F: FnOnce($($Tn,)*) -> R + Send + ,
+            F: FnOnce($($Tn,)*) -> R + MaybeSendFuture,
-            R: IntoCallToolResult + Send + ,
+            R: IntoCallToolResult + MaybeSendFuture,
-            S: Send + Sync,
+            S: MaybeSend,
         {
             #[allow(unused_variables, non_snake_case, unused_mut)]
             fn call(
                 self,
                 mut context: ToolCallContext<S>,
-            ) -> BoxFuture<'static, Result<CallToolResult, crate::ErrorData>>  {
+            ) -> MaybeBoxFuture<'static, Result<CallToolResult, crate::ErrorData>>  {
                 $(
                     let result = $Tn::from_context_part(&mut context);
                     let $Tn = match result {
                         Ok(value) => value,
-                        Err(e) => return std::future::ready(Err(e)).boxed(),
+                        Err(e) => return Box::pin(std::future::ready(Err(e))),
                     };
                 )*
-                std::future::ready(self($($Tn,)*).into_call_tool_result()).boxed()
+                Box::pin(std::future::ready(self($($Tn,)*).into_call_tool_result()))
             }
         }
     };

crates/rmcp/src/service.rs

@@ -1,6 +1,47 @@
-use futures::{FutureExt, future::BoxFuture};
+use futures::FutureExt;
+#[cfg(not(feature = "local"))]
+use futures::future::BoxFuture;
+#[cfg(feature = "local")]
+use futures::future::LocalBoxFuture;
 use thiserror::Error;
 
+// ---------------------------------------------------------------------------
+// Conditional Send helpers
+//
+// `MaybeSend`       – supertrait alias: `Send + Sync` without `local`, empty with `local`
+// `MaybeSendFuture` – future bound alias: `Send` without `local`, empty with `local`
+// `MaybeBoxFuture`  – boxed future type: `BoxFuture` without `local`, `LocalBoxFuture` with `local`
+// ---------------------------------------------------------------------------
+
+#[cfg(not(feature = "local"))]
+#[doc(hidden)]
+pub trait MaybeSend: Send + Sync {}
+#[cfg(not(feature = "local"))]
+impl<T: Send + Sync> MaybeSend for T {}
+
+#[cfg(feature = "local")]
+#[doc(hidden)]
+pub trait MaybeSend {}
+#[cfg(feature = "local")]
+impl<T> MaybeSend for T {}
+
+#[cfg(not(feature = "local"))]
+#[doc(hidden)]
+pub trait MaybeSendFuture: Send {}
+#[cfg(not(feature = "local"))]
+impl<T: Send> MaybeSendFuture for T {}
+
+#[cfg(feature = "local")]
+#[doc(hidden)]
+pub trait MaybeSendFuture {}
+#[cfg(feature = "local")]
+impl<T> MaybeSendFuture for T {}
+
+#[cfg(not(feature = "local"))]
+pub(crate) type MaybeBoxFuture<'a, T> = BoxFuture<'a, T>;
+#[cfg(feature = "local")]
+pub(crate) type MaybeBoxFuture<'a, T> = LocalBoxFuture<'a, T>;
+
 #[cfg(feature = "server")]
 use crate::model::ServerJsonRpcMessage;
 use crate::{
@@ -87,17 +128,21 @@ pub type RxJsonRpcMessage<R> = JsonRpcMessage<
     <R as ServiceRole>::PeerNot,
 >;
 
-pub trait Service<R: ServiceRole>: Send + Sync + 'static {
+#[allow(
+    private_bounds,
+    reason = "MaybeSend is a sealed conditional Send + Sync alias"
+)]
+pub trait Service<R: ServiceRole>: MaybeSend + 'static {
     fn handle_request(
         &self,
         request: R::PeerReq,
         context: RequestContext<R>,
-    ) -> impl Future<Output = Result<R::Resp, McpError>> + Send + '_;
+    ) -> impl Future<Output = Result<R::Resp, McpError>> + MaybeSendFuture + '_;
     fn handle_notification(
         &self,
         notification: R::PeerNot,
         context: NotificationContext<R>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_;
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_;
     fn get_info(&self) -> R::Info;
 }
 
@@ -111,7 +156,7 @@ pub trait ServiceExt<R: ServiceRole>: Service<R> + Sized {
     fn serve<T, E, A>(
         self,
         transport: T,
-    ) -> impl Future<Output = Result<RunningService<R, Self>, R::InitializeError>> + Send
+    ) -> impl Future<Output = Result<RunningService<R, Self>, R::InitializeError>> + MaybeSendFuture
     where
         T: IntoTransport<R, E, A>,
         E: std::error::Error + Send + Sync + 'static,
@@ -123,7 +168,7 @@ pub trait ServiceExt<R: ServiceRole>: Service<R> + Sized {
         self,
         transport: T,
         ct: CancellationToken,
-    ) -> impl Future<Output = Result<RunningService<R, Self>, R::InitializeError>> + Send
+    ) -> impl Future<Output = Result<RunningService<R, Self>, R::InitializeError>> + MaybeSendFuture
     where
         T: IntoTransport<R, E, A>,
         E: std::error::Error + Send + Sync + 'static,
@@ -135,7 +180,7 @@ impl<R: ServiceRole> Service<R> for Box<dyn DynService<R>> {
         &self,
         request: R::PeerReq,
         context: RequestContext<R>,
-    ) -> impl Future<Output = Result<R::Resp, McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<R::Resp, McpError>> + MaybeSendFuture + '_ {
         DynService::handle_request(self.as_ref(), request, context)
     }
 
@@ -143,7 +188,7 @@ impl<R: ServiceRole> Service<R> for Box<dyn DynService<R>> {
         &self,
         notification: R::PeerNot,
         context: NotificationContext<R>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         DynService::handle_notification(self.as_ref(), notification, context)
     }
 
@@ -152,17 +197,21 @@ impl<R: ServiceRole> Service<R> for Box<dyn DynService<R>> {
     }
 }
 
-pub trait DynService<R: ServiceRole>: Send + Sync {
+#[allow(
+    private_bounds,
+    reason = "MaybeSend is a sealed conditional Send + Sync alias"
+)]
+pub trait DynService<R: ServiceRole>: MaybeSend {
     fn handle_request(
         &self,
         request: R::PeerReq,
         context: RequestContext<R>,
-    ) -> BoxFuture<'_, Result<R::Resp, McpError>>;
+    ) -> MaybeBoxFuture<'_, Result<R::Resp, McpError>>;
     fn handle_notification(
         &self,
         notification: R::PeerNot,
         context: NotificationContext<R>,
-    ) -> BoxFuture<'_, Result<(), McpError>>;
+    ) -> MaybeBoxFuture<'_, Result<(), McpError>>;
     fn get_info(&self) -> R::Info;
 }
 
@@ -171,14 +220,14 @@ impl<R: ServiceRole, S: Service<R>> DynService<R> for S {
         &self,
         request: R::PeerReq,
         context: RequestContext<R>,
-    ) -> BoxFuture<'_, Result<R::Resp, McpError>> {
+    ) -> MaybeBoxFuture<'_, Result<R::Resp, McpError>> {
         Box::pin(self.handle_request(request, context))
     }
     fn handle_notification(
         &self,
         notification: R::PeerNot,
         context: NotificationContext<R>,
-    ) -> BoxFuture<'_, Result<(), McpError>> {
+    ) -> MaybeBoxFuture<'_, Result<(), McpError>> {
         Box::pin(self.handle_notification(notification, context))
     }
     fn get_info(&self) -> R::Info {
@@ -639,6 +688,28 @@ where
     serve_inner(service, transport.into_transport(), peer, peer_rx, ct)
 }
 
+/// Spawn a task that may hold `!Send` state when the `local` feature is active.
+///
+/// Without the `local` feature this is `tokio::spawn` (requires `Future: Send + 'static`).
+/// With `local` it uses `tokio::task::spawn_local` (requires only `Future: 'static`).
+#[cfg(not(feature = "local"))]
+fn spawn_service_task<F>(future: F) -> tokio::task::JoinHandle<F::Output>
+where
+    F: Future + Send + 'static,
+    F::Output: Send + 'static,
+{
+    tokio::spawn(future)
+}
+
+#[cfg(feature = "local")]
+fn spawn_service_task<F>(future: F) -> tokio::task::JoinHandle<F::Output>
+where
+    F: Future + 'static,
+    F::Output: 'static,
+{
+    tokio::task::spawn_local(future)
+}
+
 #[instrument(skip_all)]
 fn serve_inner<R, S, T>(
     service: S,
@@ -674,7 +745,7 @@ where
     let serve_loop_ct = ct.child_token();
     let peer_return: Peer<R> = peer.clone();
     let current_span = tracing::Span::current();
-    let handle = tokio::spawn(async move {
+    let handle = spawn_service_task(async move {
         let mut transport = transport.into_transport();
         let mut batch_messages = VecDeque::<RxJsonRpcMessage<R>>::new();
         let mut send_task_set = tokio::task::JoinSet::<SendTaskResult>::new();
@@ -860,7 +931,7 @@ where
                             extensions,
                         };
                         let current_span = tracing::Span::current();
-                        tokio::spawn(async move {
+                        spawn_service_task(async move {
                             let result = service
                                 .handle_request(request, context)
                                 .await;
@@ -907,7 +978,7 @@ where
                             extensions,
                         };
                         let current_span = tracing::Span::current();
-                        tokio::spawn(async move {
+                        spawn_service_task(async move {
                             let result = service.handle_notification(notification, context).await;
                             if let Err(error) = result {
                                 tracing::warn!(%error, "Error sending notification");

crates/rmcp/src/service/client.rs

@@ -162,7 +162,8 @@ impl<S: Service<RoleClient>> ServiceExt<RoleClient> for S {
         self,
         transport: T,
         ct: CancellationToken,
-    ) -> impl Future<Output = Result<RunningService<RoleClient, Self>, ClientInitializeError>> + Send
+    ) -> impl Future<Output = Result<RunningService<RoleClient, Self>, ClientInitializeError>>
+    + MaybeSendFuture
     where
         T: IntoTransport<RoleClient, E, A>,
         E: std::error::Error + Send + Sync + 'static,

crates/rmcp/src/service/server.rs

@@ -95,7 +95,8 @@ impl<S: Service<RoleServer>> ServiceExt<RoleServer> for S {
         self,
         transport: T,
         ct: CancellationToken,
-    ) -> impl Future<Output = Result<RunningService<RoleServer, Self>, ServerInitializeError>> + Send
+    ) -> impl Future<Output = Result<RunningService<RoleServer, Self>, ServerInitializeError>>
+    + MaybeSendFuture
     where
         T: IntoTransport<RoleServer, E, A>,
         E: std::error::Error + Send + Sync + 'static,

crates/rmcp/src/service/tower.rs

@@ -3,7 +3,7 @@ use std::{future::poll_fn, marker::PhantomData};
 use tower_service::Service as TowerService;
 
 use super::NotificationContext;
-use crate::service::{RequestContext, Service, ServiceRole};
+use crate::service::{MaybeSendFuture, RequestContext, Service, ServiceRole};
 
 pub struct TowerHandler<S, R: ServiceRole> {
     pub service: S,
@@ -44,7 +44,7 @@ where
         &self,
         _notification: R::PeerNot,
         _context: NotificationContext<R>,
-    ) -> impl Future<Output = Result<(), crate::ErrorData>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), crate::ErrorData>> + MaybeSendFuture + '_ {
         std::future::ready(Ok(()))
     }
 

crates/rmcp/src/transport.rs

@@ -7,7 +7,7 @@
 //! | transport         | client                                                    | server                                                |
 //! |:-:                |:-:                                                        |:-:                                                    |
 //! | std IO            | [`child_process::TokioChildProcess`]                      | [`io::stdio`]                                         |
-//! | streamable http   | [`streamable_http_client::StreamableHttpClientTransport`] | [`streamable_http_server::StreamableHttpService`]     |
+//! | streamable http   | [`streamable_http_client::StreamableHttpClientTransport`] | `streamable_http_server::StreamableHttpService`     |
 //!
 //！## Helper Transport Types
 //! Thers are several helper transport types that can help you to create transport quickly.
@@ -107,7 +107,7 @@ pub use auth::{
 // pub mod ws;
 #[cfg(feature = "transport-streamable-http-server-session")]
 pub mod streamable_http_server;
-#[cfg(feature = "transport-streamable-http-server")]
+#[cfg(all(feature = "transport-streamable-http-server", not(feature = "local")))]
 pub use streamable_http_server::tower::{StreamableHttpServerConfig, StreamableHttpService};
 
 #[cfg(feature = "transport-streamable-http-client")]

crates/rmcp/src/transport/streamable_http_server.rs

@@ -1,6 +1,6 @@
 pub mod session;
-#[cfg(feature = "transport-streamable-http-server")]
+#[cfg(all(feature = "transport-streamable-http-server", not(feature = "local")))]
 pub mod tower;
 pub use session::{SessionId, SessionManager};
-#[cfg(feature = "transport-streamable-http-server")]
+#[cfg(all(feature = "transport-streamable-http-server", not(feature = "local")))]
 pub use tower::{StreamableHttpServerConfig, StreamableHttpService};

crates/rmcp/src/transport/streamable_http_server/session.rs

@@ -33,7 +33,7 @@ pub mod never;
 
 /// Controls how MCP sessions are created, validated, and closed.
 ///
-/// The [`StreamableHttpService`](super::StreamableHttpService) calls into this
+/// The `StreamableHttpService` calls into this
 /// trait for every HTTP request that carries (or should carry) a session ID.
 ///
 /// See the [module-level docs](self) for background on sessions.

crates/rmcp/src/transport/streamable_http_server/tower.rs

@@ -204,7 +204,7 @@ impl<S, M> Clone for StreamableHttpService<S, M> {
 impl<RequestBody, S, M> tower_service::Service<Request<RequestBody>> for StreamableHttpService<S, M>
 where
     RequestBody: Body + Send + 'static,
-    S: crate::Service<RoleServer>,
+    S: crate::Service<RoleServer> + Send + 'static,
     M: SessionManager,
     RequestBody::Error: Display,
     RequestBody::Data: Send + 'static,

crates/rmcp/tests/common/handlers.rs

@@ -7,7 +7,11 @@ use std::{
 use rmcp::service::NotificationContext;
 #[cfg(feature = "client")]
 use rmcp::{ClientHandler, RoleClient};
-use rmcp::{ErrorData as McpError, RoleServer, ServerHandler, model::*, service::RequestContext};
+use rmcp::{
+    ErrorData as McpError, RoleServer, ServerHandler,
+    model::*,
+    service::{MaybeSendFuture, RequestContext},
+};
 #[cfg(feature = "client")]
 use serde_json::json;
 use tokio::sync::Notify;
@@ -85,7 +89,7 @@ impl ClientHandler for TestClientHandler {
         &self,
         params: LoggingMessageNotificationParam,
         _context: NotificationContext<RoleClient>,
-    ) -> impl Future<Output = ()> + Send + '_ {
+    ) -> impl Future<Output = ()> + MaybeSendFuture + '_ {
         let receive_signal = self.receive_signal.clone();
         let received_messages = self.received_messages.clone();
 
@@ -116,7 +120,7 @@ impl ServerHandler for TestServer {
         &self,
         request: SetLevelRequestParams,
         context: RequestContext<RoleServer>,
-    ) -> impl Future<Output = Result<(), McpError>> + Send + '_ {
+    ) -> impl Future<Output = Result<(), McpError>> + MaybeSendFuture + '_ {
         let peer = context.peer;
         async move {
             let (data, logger) = match request.level {

crates/rmcp/tests/test_client_initialization.rs

@@ -1,5 +1,5 @@
 // cargo test --features "server client" --package rmcp test_client_initialization
-#![cfg(feature = "client")]
+#![cfg(all(feature = "client", not(feature = "local")))]
 
 mod common;
 

crates/rmcp/tests/test_close_connection.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 //cargo test --test test_close_connection --features "client server"
 
 mod common;

crates/rmcp/tests/test_custom_headers.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::collections::HashMap;
 
 use http::{HeaderName, HeaderValue};

crates/rmcp/tests/test_custom_request.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::sync::Arc;
 
 use rmcp::{

crates/rmcp/tests/test_logging.rs

@@ -1,4 +1,5 @@
 // cargo test --features "server client" --package rmcp test_logging
+#![cfg(not(feature = "local"))]
 mod common;
 
 use std::sync::{Arc, Mutex};

crates/rmcp/tests/test_message_protocol.rs

@@ -1,4 +1,5 @@
 //cargo test --test test_message_protocol --features "client server"
+#![cfg(not(feature = "local"))]
 
 mod common;
 use common::handlers::{TestClientHandler, TestServer};

crates/rmcp/tests/test_notification.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::sync::Arc;
 
 use rmcp::{

crates/rmcp/tests/test_progress_subscriber.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use futures::StreamExt;
 use rmcp::{
     ClientHandler, Peer, RoleServer, ServerHandler, ServiceExt,

crates/rmcp/tests/test_prompt_macros.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 //cargo test --test test_prompt_macros --features "client server"
 #![allow(dead_code)]
 use std::sync::Arc;

crates/rmcp/tests/test_prompt_routers.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::collections::HashMap;
 
 use futures::future::BoxFuture;

crates/rmcp/tests/test_sampling.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 mod common;
 
 use anyhow::Result;

crates/rmcp/tests/test_server_initialization.rs

@@ -1,5 +1,5 @@
 // cargo test --features "client" --package rmcp -- server_init
-#![cfg(feature = "client")]
+#![cfg(all(feature = "client", not(feature = "local")))]
 mod common;
 
 use common::handlers::TestServer;

crates/rmcp/tests/test_sse_concurrent_streams.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 /// Tests for concurrent SSE stream handling (shadow channels)
 ///
 /// These tests verify that multiple GET SSE streams on the same session

crates/rmcp/tests/test_streamable_http_json_response.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use rmcp::transport::streamable_http_server::{
     StreamableHttpServerConfig, StreamableHttpService, session::local::LocalSessionManager,
 };

crates/rmcp/tests/test_streamable_http_priming.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::time::Duration;
 
 use rmcp::transport::streamable_http_server::{

crates/rmcp/tests/test_streamable_http_stale_session.rs

@@ -1,7 +1,8 @@
 #![cfg(all(
     feature = "transport-streamable-http-client",
     feature = "transport-streamable-http-client-reqwest",
-    feature = "transport-streamable-http-server"
+    feature = "transport-streamable-http-server",
+    not(feature = "local")
 ))]
 
 use std::{collections::HashMap, sync::Arc};

crates/rmcp/tests/test_task_support_validation.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 //! Tests for task support validation in tool calls.
 //!
 //! Verifies that the server correctly validates `execution.taskSupport` settings

crates/rmcp/tests/test_tool_macros.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 //! Test tool macros, including documentation for generated fns.
 
 //cargo test --test test_tool_macros --features "client server"

crates/rmcp/tests/test_tool_routers.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::collections::HashMap;
 
 use futures::future::BoxFuture;

crates/rmcp/tests/test_with_js.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use rmcp::{
     ServiceExt,
     service::QuitReason,

crates/rmcp/tests/test_with_python.rs

@@ -1,3 +1,4 @@
+#![cfg(not(feature = "local"))]
 use std::process::Stdio;
 
 use rmcp::{