MCP TypeScript SDK

Important

This is the main branch: v2 of the SDK (@modelcontextprotocol/server, @modelcontextprotocol/client), the stable release line, implementing the 2026-07-28 MCP spec. Start with the v2 documentation; coming from v1, see the migration guide.

v1.x (@modelcontextprotocol/sdk) lives on the v1.x branch and continues to receive bug fixes and security updates for at least six months after the v2 release (2026-07-27). Its documentation is at ts.sdk.modelcontextprotocol.io.

Found a problem in v2? Open an issue.

Note

Contributors without write access can have one open pull request at a time. Draft pull requests don't count toward the limit. For a feature or a larger change, please open an issue first; see CONTRIBUTING.md.

Table of Contents

• Overview
• Packages
• Installation
• Getting Started
• Documentation
• Contributing
• License

Overview

The Model Context Protocol (MCP) allows applications to provide context for LLMs in a standardized way, separating the concerns of providing context from the actual LLM interaction.

This repository contains the TypeScript SDK implementation of the MCP specification. It runs on Node.js, Bun, and Deno, and ships:

• MCP server libraries (tools/resources/prompts, Streamable HTTP, stdio, auth helpers)
• MCP client libraries (transports, high-level helpers, OAuth helpers)
• Optional middleware packages for specific runtimes/frameworks (Express, Fastify, Hono, Node.js HTTP)
• Runnable examples (under examples/)

Packages

This monorepo publishes split packages:

• @modelcontextprotocol/server: build MCP servers
• @modelcontextprotocol/client: build MCP clients

Tool and prompt schemas use Standard Schema — bring Zod v4, Valibot, ArkType, or any compatible library.

Middleware packages (optional)

The SDK also publishes small "middleware" packages under packages/middleware/ that help you wire MCP into a specific runtime or web framework.

They are intentionally thin adapters: they should not introduce new MCP functionality or business logic. See packages/middleware/README.md for details.

• @modelcontextprotocol/node: Node.js Streamable HTTP transport wrapper for IncomingMessage / ServerResponse
• @modelcontextprotocol/express: Express helpers (app defaults + Host header validation)
• @modelcontextprotocol/fastify: Fastify helpers (app defaults + Host header validation)
• @modelcontextprotocol/hono: Hono helpers (app defaults + JSON body parsing hook + Host header validation)

Installation

Server

npm install @modelcontextprotocol/server
# or
bun add @modelcontextprotocol/server
# or
deno add npm:@modelcontextprotocol/server

Client

npm install @modelcontextprotocol/client
# or
bun add @modelcontextprotocol/client
# or
deno add npm:@modelcontextprotocol/client

Optional middleware packages

The SDK also publishes optional “middleware” packages that help you wire MCP into a specific runtime or web framework (for example Express, Fastify, Hono, or Node.js http).

These packages are intentionally thin adapters and should not introduce additional MCP features or business logic. See packages/middleware/README.md for details.

# Node.js HTTP (IncomingMessage/ServerResponse) Streamable HTTP transport:
npm install @modelcontextprotocol/node

# Express integration:
npm install @modelcontextprotocol/express express

# Fastify integration:
npm install @modelcontextprotocol/fastify fastify

# Hono integration:
npm install @modelcontextprotocol/hono hono

Getting Started

Here is what an MCP server looks like. This minimal example exposes a single greet tool over stdio:

import { McpServer } from '@modelcontextprotocol/server';
import { StdioServerTransport } from '@modelcontextprotocol/server/stdio';
import * as z from 'zod/v4';

const server = new McpServer({ name: 'greeting-server', version: '1.0.0' });

server.registerTool(
    'greet',
    {
        description: 'Greet someone by name',
        inputSchema: z.object({ name: z.string() })
    },
    async ({ name }) => ({
        content: [{ type: 'text', text: `Hello, ${name}!` }]
    })
);

async function main() {
    const transport = new StdioServerTransport();
    await server.connect(transport);
}

main();

Ready to build something real? Follow the step-by-step tutorials:

• Build your first server — a stdio weather-alert server, from npm init to a tool call
• Build your first client — connect to that server, list its tools, and call them

For runnable, end-to-end examples beyond the tutorials, see:

• examples/README.md — runnable, self-verifying client/server example pairs (one story per directory)

Documentation

• Build a server — your first MCP server, step by step
• Build a client — your first MCP client, step by step
• Documentation site — the full guides: tools, resources, prompts, serving over HTTP and stdio, clients, OAuth, and migration
• Troubleshooting — common errors and their fixes
• API reference
• MCP documentation
• MCP specification

Building docs locally

To work on the documentation site locally:

pnpm docs:api      # Generate the API reference markdown (output: docs/api/)
pnpm docs:dev      # Start the VitePress dev server for the V2 site
pnpm docs:build    # Build the V2 site (output: docs/.vitepress/dist/)
pnpm docs:multi    # Build the combined V1 + V2 site (output: tmp/docs-combined/)

The docs:multi script builds the V2 site from the current checkout, checks out the v1.x branch via a git worktree to build the V1 site, and produces a combined site with V1 docs at the root and V2 docs under /v2/.

v1 (legacy) documentation and fixes

If you are using the v1 generation of the SDK, the v1 API documentation is available at https://ts.sdk.modelcontextprotocol.io/. The v1 source code and any v1-specific fixes live on the long-lived v1.x branch. V2 API docs are at /v2/.

Contributing

Issues and pull requests are welcome on GitHub at https://github.com/modelcontextprotocol/typescript-sdk.

License

This project is licensed under the Apache License 2.0 for new contributions, with existing code under MIT. See the LICENSE file for details.