Hello World MCP Server

A simple Model Context Protocol (MCP) server implementation built with TypeScript. This server demonstrates basic MCP functionality including resources, prompts, and tools.

Features

• SSE and STDIO transport support
• Resource handling with static and dynamic resources
• Sample prompt implementation
• Example tool that echoes messages
• Debug tool for server introspection

Getting Started

Prerequisites

• Node.js (v16 or higher)
• npm or yarn

Installation

npm install

Build

npm run build

Running the Server

HTTP/SSE Transport (Web Browsers)

npm run start:http

This starts the server on http://localhost:3000 with:

• SSE endpoint at /sse
• Message endpoint at /messages

STDIO Transport (Command Line)

npm run start

This runs the server in stdio mode for command-line integrations.

Testing the Server

Testing with cURL

1. Start the HTTP server:

   npm run start:http

2. In a terminal window, connect to the SSE endpoint:

   curl -N http://localhost:3000/sse

   You should see a response like:

   event: endpoint
   data: /messages?sessionId=YOUR_SESSION_ID
   

3. In another terminal window, send a request to invoke the echo tool:

   curl -X POST \
     "http://localhost:3000/messages?sessionId=YOUR_SESSION_ID" \
     -H 'Content-Type: application/json' \
     -d '{
       "jsonrpc": "2.0",
       "id": 1,
       "method": "tools/invoke",
       "params": {
         "name": "echo",
         "parameters": {
           "message": "Testing the MCP server!"
         }
       }
     }'

4. You should see a response in the SSE terminal window:

   event: message
   data: {"jsonrpc":"2.0","id":1,"result":{"content":[{"type":"text","text":"Hello Testing the MCP server!"}]}}
   

5. Try the debug tool to see available server methods:

   curl -X POST \
     "http://localhost:3000/messages?sessionId=YOUR_SESSION_ID" \
     -H 'Content-Type: application/json' \
     -d '{
       "jsonrpc": "2.0",
       "id": 2,
       "method": "tools/invoke",
       "params": {
         "name": "debug",
         "parameters": {}
       }
     }'

Testing with MCP Inspector

For a visual interface, you can use the MCP Inspector tool:

1. Connect to http://localhost:3000/sse in the MCP Inspector
2. Browse available resources and tools
3. Invoke tools interactively

Server API

Resources

• hello://world - A static hello world resource
• greeting://{name} - A dynamic greeting with a name parameter

Tools

• echo - Echoes back a message with "Hello" prefix
• debug - Lists all available tools and methods

Prompts

• helpful-assistant - A basic helpful assistant prompt

Troubleshooting

• If you get "Headers already sent" errors, make sure you're not manually setting headers
• Session ID handling is crucial for proper message routing
• Check the server console for debugging information

License

MIT