expressjs-mcp

express_mcp

Expose your Express endpoints as MCP tools (mount to your app or run a standalone HTTP gateway), preserving schemas and auth behavior.

• Inspiration: FastAPI-MCP — https://github.com/tadata-org/fastapi_mcp

Features

• Zero Configuration: Works out-of-the-box with existing Express apps
• Schema Preservation: Supports OpenAPI v3 and zod annotations
• Auth Integration: Reuses existing Express middleware (no bypass)
• Flexible Deployment: Mount to same app or run standalone
• In-Process Efficiency: Direct middleware execution (no HTTP overhead)
• 🚀 Streaming Support: Handle Server-Sent Events, file downloads, and real-time data
• 📦 NPX/Bunx Commands: Easy CLI access with npx expressjs-mcp and bunx expressjs-mcp

Installation

Option 1: Install from npm (Recommended)

# Install globally or locally
npm install -g expressjs-mcp
# or with pnpm
pnpm add -g expressjs-mcp

# Use with npx (no installation required)
npx expressjs-mcp init

Option 2: Clone and build locally

git clone https://github.com/bowen31337/expressjs_mcp.git
cd expressjs_mcp
pnpm install && pnpm build

Quick Start

Option 1: CLI Commands (Recommended)

# Initialize in your project (works with npm package or locally built)
npx expressjs-mcp init
# or if installed locally: node bin/express-mcp.cjs init

# Start your server
node server.js

# Test connection
npx expressjs-mcp test --url http://localhost:3000/mcp
# or if installed locally: node bin/express-mcp.cjs test --url http://localhost:3000/mcp

Option 2: Manual Setup

npm install expressjs-mcp
# or
pnpm add expressjs-mcp

import express from 'express';
import { ExpressMCP } from 'expressjs-mcp';

const app = express();
app.use(express.json());

app.get('/hello', (_req, res) => res.json({ message: 'world' }));

const mcp = new ExpressMCP(app, { mountPath: '/mcp' });
await mcp.init();
mcp.mount('/mcp');

Streaming Support

Express MCP supports three types of streaming for real-time data:

🌊 1. HTTP Chunked Streaming

app.get('/api/chunked', (req, res) => {
  res.setHeader('Transfer-Encoding', 'chunked');
  res.write('Processing...\n');
  // Stream data in chunks
});

📡 2. Server-Sent Events (SSE)

app.get('/api/sse', (req, res) => {
  res.setHeader('Content-Type', 'text/event-stream');
  res.setHeader('Cache-Control', 'no-cache');
  
  let count = 0;
  const interval = setInterval(() => {
    res.write(`data: ${JSON.stringify({ count: ++count })}\n\n`);
    if (count >= 10) {
      clearInterval(interval);
      res.end();
    }
  }, 1000);
});

📄 3. NDJSON/JSON Lines

app.get('/api/ndjson', (req, res) => {
  res.setHeader('Content-Type', 'application/x-ndjson');
  
  const data = [{ id: 1 }, { id: 2 }];
  data.forEach(item => {
    res.write(JSON.stringify(item) + '\n');
  });
  res.end();
});

Testing All Streaming Types

# HTTP Streaming via MCP
curl -X POST http://localhost:3000/mcp/invoke \
  -H "Content-Type: application/json" \
  -d '{"toolName": "GET /api/stream", "args": {}, "streaming": true}'

# stdio Streaming via MCP Bridge (npm package)
echo '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"GET /api/ndjson","arguments":{"_streaming":true}}}' | \
  npx expressjs-mcp bridge
  
# Or with local installation:
echo '{"jsonrpc":"2.0","id":1,"method":"tools/call","params":{"name":"GET /api/ndjson","arguments":{"_streaming":true}}}' | \
  node /path/to/your/expressjs_mcp/scripts/mcp-bridge.cjs

# Direct endpoint testing
curl http://localhost:3000/api/sse        # SSE
curl http://localhost:3000/api/ndjson     # NDJSON
curl http://localhost:3000/api/chunked    # Chunked

Documentation

• 🚀 Quick MCP Setup - Get started in 3 steps
• 📁 Examples & Tutorials - Complete example walkthroughs
• 🔧 Working MCP Configurations - IMPORTANT: Working configs before npm publish
• 🚀 Publishing & CI/CD - Automated npm publishing workflow
• MCP Client Setup - Detailed configuration guide
• Streaming Guide - Comprehensive streaming documentation
• Usage Guide - API reference and examples
• Architecture - Technical overview
• PRD - Product requirements

Development

pnpm install
pnpm test      # Run tests
pnpm build     # Build for production
pnpm lint      # Check code quality

Configuration Options

• OpenAPI: Provide your OpenAPI v3 spec for rich schemas
• Schema Annotations: Use zod for per-route type validation
• Route Filtering: Include/exclude specific endpoints
• Auth Preservation: Existing middleware runs unchanged
• Streaming: Automatic detection and handling of streaming responses
• Timeouts: Configurable request timeouts for long-running operations