RMCP

An official Rust Model Context Protocol SDK implementation with tokio async runtime.

Migrating to 3.x? See the migration guide for breaking changes and upgrade instructions.

This repository contains the following crates:

• rmcp: The core crate providing the RMCP protocol implementation - see rmcp
• rmcp-macros: A procedural macro crate for generating RMCP tool implementations - see rmcp-macros

This SDK implements the stable MCP 2026-07-28 specification while remaining fully compatible with the 2025-11-25 release and earlier versions. Features introduced in 2026-07-28 — server discovery & negotiation, transport-neutral subscriptions, long-running tasks, response caching, multi-round-trip requests, and standard HTTP routing headers — are documented below. For the full MCP specification, see modelcontextprotocol.io.

Table of Contents

• Usage
• Tools
• Resources
• Prompts
• Sampling
• Elicitation
• Roots
• Logging
• Completions
• Notifications
• Subscriptions
• Multi-Round-Trip Requests
• Tasks
• Caching
• Standard HTTP Headers
• Stateless Streamable HTTP
• Transports
• Pagination
• Capability & Protocol Version Negotiation
• JSON Schema 2020-12
• Examples
• OAuth Support
• Related Resources
• Related Projects
• Development

Usage

Import the crate

Add the latest published version with cargo:

cargo add rmcp --features server

Or use the dev channel:

cargo add rmcp --features server --git https://github.com/modelcontextprotocol/rust-sdk --branch main

Third Dependencies

Basic dependencies:

• tokio
• serde Json Schema generation (version 2020-12):
• schemars

Build a Client

Start a client

use rmcp::{ServiceExt, transport::{TokioChildProcess, ConfigureCommandExt}};
use tokio::process::Command;

#[tokio::main]
async fn main() -> Result<(), Box<dyn std::error::Error>> {
    let client = ().serve(TokioChildProcess::new(Command::new("npx").configure(|cmd| {
        cmd.arg("-y").arg("@modelcontextprotocol/server-everything");
    }))?).await?;
    Ok(())
}

Client lifecycle modes

serve() uses the legacy MCP lifecycle: the client sends initialize, receives the negotiated server information, and then sends notifications/initialized. Use ClientServiceExt::serve_with_lifecycle to select another lifecycle explicitly:

use rmcp::{ClientLifecycleMode, ClientServiceExt, ProtocolVersion, model::ClientConfig};