typescript-sdk/packages/middleware/express

@modelcontextprotocol/express

Express adapters for the MCP TypeScript server SDK.

This package is a thin Express integration layer for @modelcontextprotocol/server.

It does not implement MCP itself. Instead, it helps you:

• create an Express app with sensible defaults for MCP servers
• add DNS rebinding protection via Host header validation (recommended for localhost servers)

Install

npm install @modelcontextprotocol/server @modelcontextprotocol/express express

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

Exports

• createMcpExpressApp(options?)
• hostHeaderValidation(allowedHostnames)
• localhostHostValidation()

Usage

Create an Express app (localhost DNS rebinding protection by default)

import { createMcpExpressApp } from '@modelcontextprotocol/express';

const app = createMcpExpressApp(); // default host is 127.0.0.1; protection enabled

Streamable HTTP endpoint (Express)

import { createMcpExpressApp } from '@modelcontextprotocol/express';
import { NodeStreamableHTTPServerTransport } from '@modelcontextprotocol/node';
import { McpServer } from '@modelcontextprotocol/server';

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

app.post('/mcp', async (req, res) => {
    // Stateless example: create a transport per request.
    // For stateful mode (sessions), keep a transport instance around and reuse it.
    const transport = new NodeStreamableHTTPServerTransport({ sessionIdGenerator: undefined });
    await server.connect(transport);
    await transport.handleRequest(req, res, req.body);
});

Host header validation (DNS rebinding protection)

import { hostHeaderValidation } from '@modelcontextprotocol/express';

app.use(hostHeaderValidation(['localhost', '127.0.0.1', '[::1]']));