Crate tower_mcp 

tower-mcp

Tower-native Model Context Protocol (MCP) implementation for Rust.

This crate provides a composable, middleware-friendly approach to building MCP servers and clients using the Tower service abstraction.

Philosophy

Unlike framework-style MCP implementations, tower-mcp treats MCP as just another protocol that can be served through Tower’s Service trait. This means:

• Standard tower middleware (tracing, metrics, rate limiting, auth) just works
• Same service can be exposed over multiple transports (stdio, HTTP, WebSocket)
• Easy integration with existing tower-based applications (axum, tonic, etc.)

Quick Start: Server

Build an MCP server with tools, resources, and prompts:

use tower_mcp::{BoxError, McpRouter, ToolBuilder, CallToolResult, StdioTransport};
use schemars::JsonSchema;
use serde::Deserialize;

#[derive(Debug, Deserialize, JsonSchema)]
struct GreetInput {
    name: String,
}

#[tokio::main]
async fn main() -> Result<(), BoxError> {
    // Define a tool
    let greet = ToolBuilder::new("greet")
        .description("Greet someone by name")
        .handler(|input: GreetInput| async move {
            Ok(CallToolResult::text(format!("Hello, {}!", input.name)))
        })
        .build()?;

    // Create router and run over stdio
    let router = McpRouter::new()
        .server_info("my-server", "1.0.0")
        .tool(greet);

    StdioTransport::new(router).run().await?;
    Ok(())
}

Quick Start: Client

Connect to an MCP server and call tools:

use tower_mcp::BoxError;
use tower_mcp::client::{McpClient, StdioClientTransport};

#[tokio::main]
async fn main() -> Result<(), BoxError> {
    // Connect to server
    let transport = StdioClientTransport::spawn("my-mcp-server", &[]).await?;
    let mut client = McpClient::new(transport);

    // Initialize and list tools
    client.initialize("my-client", "1.0.0").await?;
    let tools = client.list_tools().await?;

    // Call a tool
    let result = client.call_tool("greet", serde_json::json!({"name": "World"})).await?;
    println!("{:?}", result);

    Ok(())
}

Key Types

Server

• McpRouter - Routes MCP requests to tools, resources, and prompts
• ToolBuilder - Builder for defining tools with type-safe handlers
• ResourceBuilder - Builder for defining resources
• PromptBuilder - Builder for defining prompts
• StdioTransport - Stdio transport for CLI servers

Client

• McpClient - Client for connecting to MCP servers
• StdioClientTransport - Spawn and connect to server subprocesses

Protocol

• CallToolResult - Tool execution result with content
• ReadResourceResult - Resource read result
• GetPromptResult - Prompt expansion result
• Content - Text, image, audio, or resource content

Feature Flags

• full - Enable all optional features
• http - HTTP/SSE transport for web servers
• websocket - WebSocket transport for bidirectional communication
• childproc - Child process transport for subprocess management
• oauth - OAuth 2.1 resource server support (token validation, metadata endpoint)
• testing - Test utilities ([TestClient]) for ergonomic MCP server testing

MCP Specification

This crate implements the MCP specification (2025-11-25): https://modelcontextprotocol.io/specification/2025-11-25

Re-exports

pub use async_task::Task;

pub use async_task::TaskStore;

pub use client::ClientTransport;

pub use client::McpClient;

pub use client::StdioClientTransport;

pub use context::ChannelClientRequester;

pub use context::ClientRequester;

pub use context::ClientRequesterHandle;

pub use context::NotificationReceiver;

pub use context::NotificationSender;

pub use context::OutgoingRequest;

pub use context::OutgoingRequestReceiver;

pub use context::OutgoingRequestSender;

pub use context::RequestContext;

pub use context::RequestContextBuilder;

pub use context::ServerNotification;

pub use context::outgoing_request_channel;

pub use error::BoxError;

pub use error::Error;

pub use error::Result;

pub use error::ToolError;

pub use jsonrpc::JsonRpcLayer;

pub use jsonrpc::JsonRpcService;

pub use prompt::Prompt;

pub use prompt::PromptBuilder;

pub use prompt::PromptHandler;

pub use protocol::CallToolResult;

pub use protocol::CompleteParams;

pub use protocol::CompleteResult;

pub use protocol::Completion;

pub use protocol::CompletionArgument;

pub use protocol::CompletionReference;

pub use protocol::CompletionsCapability;

pub use protocol::Content;

pub use protocol::ContentRole;

pub use protocol::CreateMessageParams;

pub use protocol::CreateMessageResult;

pub use protocol::ElicitAction;

pub use protocol::ElicitFieldValue;

pub use protocol::ElicitFormParams;

pub use protocol::ElicitFormSchema;

pub use protocol::ElicitMode;

pub use protocol::ElicitRequestParams;

pub use protocol::ElicitResult;

pub use protocol::ElicitUrlParams;

pub use protocol::ElicitationCapability;

pub use protocol::ElicitationCompleteParams;

pub use protocol::GetPromptResult;

pub use protocol::GetPromptResultBuilder;

pub use protocol::IncludeContext;

pub use protocol::JsonRpcMessage;

pub use protocol::JsonRpcRequest;

pub use protocol::JsonRpcResponse;

pub use protocol::JsonRpcResponseMessage;

pub use protocol::ListRootsParams;

pub use protocol::ListRootsResult;

pub use protocol::McpRequest;

pub use protocol::McpResponse;

pub use protocol::ModelHint;

pub use protocol::ModelPreferences;

pub use protocol::PrimitiveSchemaDefinition;

pub use protocol::PromptMessage;

pub use protocol::PromptReference;

pub use protocol::PromptRole;

pub use protocol::ReadResourceResult;

pub use protocol::ResourceContent;

pub use protocol::ResourceReference;

pub use protocol::Root;

pub use protocol::RootsCapability;

pub use protocol::SamplingCapability;

pub use protocol::SamplingContent;

pub use protocol::SamplingContentOrArray;

pub use protocol::SamplingMessage;

pub use protocol::SamplingTool;

pub use protocol::ToolChoice;

pub use resource::Resource;

pub use resource::ResourceBuilder;

pub use resource::ResourceHandler;

pub use resource::ResourceTemplate;

pub use resource::ResourceTemplateBuilder;

pub use resource::ResourceTemplateHandler;

pub use router::Extensions;

pub use router::McpRouter;

pub use router::RouterRequest;

pub use router::RouterResponse;

pub use session::SessionPhase;

pub use session::SessionState;

pub use tool::Tool;

pub use tool::ToolBuilder;

pub use tool::ToolHandler;

pub use transport::BidirectionalStdioTransport;

pub use transport::CatchError;

pub use transport::GenericStdioTransport;

pub use transport::StdioTransport;

pub use transport::SyncStdioTransport;

Modules

async_task

Async task management for long-running MCP operations

auth

Authentication middleware helpers for MCP servers

client

MCP Client implementation

context

Request context for MCP handlers

error

Error types for tower-mcp

jsonrpc

JSON-RPC 2.0 service layer

prompt

Prompt definition and builder API

protocol

MCP protocol types based on JSON-RPC 2.0

resource

Resource definition and builder API

router

MCP Router - routes requests to tools, resources, and prompts

session

MCP session state management

tool

Tool definition and builder API

transport

MCP transport implementations