Struct McpServerBuilder 

pub struct McpServerBuilder<Counterpart: Role, Responder>
where
    Responder: RunWithConnectionTo<Counterpart>,
{ /* private fields */ }

Builder for creating MCP servers with tools.

Use McpServer::builder to create a new builder, then chain methods to configure the server and call build to create the server.

Example

let server = McpServer::builder("my-server".to_string())
    .instructions("A helpful assistant")
    .tool(EchoTool)
    .tool_fn(
        "greet",
        "Greet someone by name",
        async |input: GreetInput, _cx| Ok(format!("Hello, {}!", input.name)),
        agent_client_protocol::tool_fn!(),
    )
    .build();

Implementations

impl<Counterpart: Role, Responder> McpServerBuilder<Counterpart, Responder>

where Responder: RunWithConnectionTo<Counterpart>,

pub fn instructions(self, instructions: impl ToString) -> Self

Set the server instructions that are provided to the client.

pub fn tool(self, tool: impl McpTool<Counterpart> + 'static) -> Self

Add a tool to the server.

pub fn disable_all_tools(self) -> Self

Disable all tools. After calling this, only tools explicitly enabled with enable_tool will be available.

pub fn enable_all_tools(self) -> Self

Enable all tools. After calling this, all tools will be available except those explicitly disabled with disable_tool.

pub fn disable_tool(self, name: &str) -> Result<Self, Error>

Disable a specific tool by name.

Returns an error if the tool is not registered.

pub fn enable_tool(self, name: &str) -> Result<Self, Error>

Enable a specific tool by name.

Returns an error if the tool is not registered.

pub fn tool_fn_mut<P, Ret, F>( self, name: impl ToString, description: impl ToString, func: F, tool_future_hack: impl for<'a> Fn(&'a mut F, P, McpConnectionTo<Counterpart>) -> BoxFuture<'a, Result<Ret, Error>> + Send + 'static, ) -> McpServerBuilder<Counterpart, impl RunWithConnectionTo<Counterpart>>

where P: JsonSchema + DeserializeOwned + 'static + Send, Ret: JsonSchema + Serialize + 'static + Send, F: AsyncFnMut(P, McpConnectionTo<Counterpart>) -> Result<Ret, Error> + Send,

Convenience wrapper for defining a “single-threaded” tool without having to create a struct. By “single-threaded”, we mean that only one invocation of the tool can be running at a time. Typically agents invoke a tool once per session and then block waiting for the result, so this is fine, but they could attempt to run multiple invocations concurrently, in which case those invocations would be serialized.

Parameters

• name: The name of the tool.
• description: The description of the tool.
• func: The function that implements the tool. Use an async closure like async |args, cx| { .. }.

Examples

McpServer::builder("my-server")
    .tool_fn_mut(
        "greet",
        "Greet someone by name",
        async |input: GreetInput, _cx| Ok(format!("Hello, {}!", input.name)),
    )

pub fn tool_fn<P, Ret, F>( self, name: impl ToString, description: impl ToString, func: F, tool_future_hack: impl for<'a> Fn(&'a F, P, McpConnectionTo<Counterpart>) -> BoxFuture<'a, Result<Ret, Error>> + Send + Sync + 'static, ) -> McpServerBuilder<Counterpart, impl RunWithConnectionTo<Counterpart>>

where P: JsonSchema + DeserializeOwned + 'static + Send, Ret: JsonSchema + Serialize + 'static + Send, F: AsyncFn(P, McpConnectionTo<Counterpart>) -> Result<Ret, Error> + Send + Sync + 'static,

Convenience wrapper for defining a stateless tool that can run concurrently. Unlike tool_fn_mut, multiple invocations of this tool can run at the same time since the function is Fn rather than FnMut.

Parameters

• name: The name of the tool.
• description: The description of the tool.
• func: The function that implements the tool. Use an async closure like async |args, cx| { .. }.

Examples

McpServer::builder("my-server")
    .tool_fn(
        "greet",
        "Greet someone by name",
        async |input: GreetInput, _cx| Ok(format!("Hello, {}!", input.name)),
    )

pub fn build(self) -> McpServer<Counterpart, Responder>

Create an MCP server from this builder.

This builder can be attached to new sessions (see SessionBuilder::with_mcp_server) or served up as part of a proxy (see Builder::with_mcp_server).

Trait Implementations

impl<Counterpart: Debug + Role, Responder> Debug for McpServerBuilder<Counterpart, Responder>

where Responder: RunWithConnectionTo<Counterpart> + Debug,

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.