Express MCP Server

A clean, modular implementation of the Model Context Protocol (MCP) using Express.js and TypeScript.

Quick Start

# Install dependencies
npm install

# Development (with file watching)
npm run dev

# Production
npm run build
npm start

# Type checking
npm run type-check

Server runs on http://localhost:3001

Related MCP server: MCP Server Basic Example

Endpoints

• Health: GET /mcp/health - Server health status

• Info: GET /mcp/info - Server information and capabilities

• MCP Protocol: POST/GET/DELETE /mcp - Main MCP endpoints with streaming support

Project Structure

src/
├── index.ts              Entry point - starts the server
├── app.ts                Express app factory
├── server/
│   └── mcp.ts            Core MCP server logic
├── routes/
│   └── mcp.ts            HTTP route handlers
└── tools/
    └── index.ts          Tool definitions

Total: 201 lines of focused, readable code

Architecture

Single Responsibility Principle

Each module has one clear purpose:

• index.ts (10 lines) - Server startup

• app.ts (20 lines) - Express setup

• server/mcp.ts (60 lines) - MCP protocol handling

• routes/mcp.ts (69 lines) - HTTP routing

• tools/index.ts (42 lines) - Tool catalog

Features

✓ Official MCP SDK integration (StreamableHTTPServerTransport) ✓ HTTP streaming (chunked encoding + Server-Sent Events) ✓ Session management with automatic UUID generation ✓ Zod schema validation for tool inputs ✓ Comprehensive error handling ✓ Health check and info endpoints ✓ TypeScript strict mode

Tools

Three example tools are included:

1. add(a, b) - Add two numbers

2. multiply(x, y) - Multiply two numbers

3. echo(message) - Echo a message

Adding a New Tool

Edit src/tools/index.ts and add to the array:

{
  name: "my-tool",
  description: "What this tool does",
  inputSchema: {
    param1: z.string().describe("Parameter description"),
    param2: z.number().describe("Another parameter"),
  },
  handler: async (args) => {
    const p1 = args.param1 as string;
    const p2 = args.param2 as number;
    // Tool logic here
    return `Result: ${p1} ${p2}`;
  },
}

Then rebuild:

npm run build
npm start

Testing

# Health check
curl http://localhost:3001/mcp/health

# Server info
curl http://localhost:3001/mcp/info

# MCP protocol request (with proper headers)
curl -X POST http://localhost:3001/mcp \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -d '{"jsonrpc":"2.0","id":1,"method":"tools/list","params":{}}'

Development

# Watch mode (recompiles on file changes)
npm run dev

# Type checking only
npm run type-check

# Build production bundle
npm run build

Environment Variables

• PORT (default: 3001) - Server port

PORT=4000 npm start

Stack

• Express.js - Web framework

• TypeScript - Type safety

• Zod - Schema validation

• MCP SDK - Protocol implementation

• Node.js 18+ - Runtime

Standards

• MCP Protocol Version: 2024-11-05

• HTTP Streaming: Chunked encoding + SSE

• Schema Validation: Zod

• Code Format: TypeScript with strict mode

• Code Style: Tabs, consistent formatting

Documentation

• ARCHITECTURE.md - Detailed architecture overview

• QUICK_START.md - 5-minute setup guide

• COMMANDS.md - Command reference

• REFACTORING_SUMMARY.md - Development history

License

MIT