prabha-lead/mcp-with-express

Wrapping MCP server with Express

Overview

MCP (Model Context Protocol) is a framework that enables custom tools to be integrated into AI-powered development environments like Cursor AI. Tools exposed via MCP can fetch external data, automate tasks, or interact with services on behalf of the developer.

This project demonstrates how to wrap an MCP server with an Express.js API. Specifically, it uses:

• An MCP server exposing two tools:
  • getServerName: returns the server name from environment
  • getWeatherByCity: returns weather info for a given city
• An Express REST API that fetches weather data using https://wttr.in (a free weather service)
• A concurrently-based setup to run both servers simultaneously
• A mcp.json file for Cursor IDE integration

Requirements

• Node.js: Version 20 or higher
• Cursor IDE: With Agent Mode enabled

Features

• ✅ MCP + Express Integration
  MCP tools interact with a local Express server, enabling clean separation of tool logic and HTTP services.

• 🌦️ Weather by City Tool
  The getWeatherByCity tool fetches weather data from wttr.in through an Express route.

• 🧠 Environment-Driven Server Name Tool
  The getServerName tool returns the current server name via an environment variable.

• 📦 Zod Validation
  Input validation is handled with Zod.

• 🔄 StdioServerTransport
  Cursor IDE communicates with the MCP server using standard I/O.

Installation

1. Clone the Repository

git clone <your-repo-url>
cd mcp-server-node

2. Install Dependencies

npm install

Running the Server

Use the start script to launch both MCP and Express servers together:

npm start

This runs:

• mcp-server.js: MCP tool definitions
• express-api.js: Express REST endpoint for weather

Cursor IDE Integration

To connect this project to Cursor:

1. Create a mcp.json file

Place this in the root of your project:

{
  "mcpServers": {
    "mcp-with-express": {
      "command": "/absolute/path/to/node",
      "args": ["/absolute/path/to/mcp-server.js"],
      "env": {
        "SERVER_NAME": "mcp-with-express"
      }
    }
  }
}

Getting Absolute Paths

To correctly set up the mcp.json file, you need the absolute paths for the Node.js executable and the mcp-server.js file. Here's how you can find these paths on different operating systems:

On macOS:

1. Node.js Path:

   • Open Terminal.
   • Run the command: which node
   • This will output the absolute path to the Node.js executable.

2. mcp-server.js Path:

   • In Terminal, navigate to your project directory using cd /path/to/your/project.
   • Run the command: pwd
   • Append /mcp-server.js to the output to get the full path.

On Windows:

1. Node.js Path:

   • Open Command Prompt.
   • Run the command: where node
   • This will output the absolute path to the Node.js executable.

2. mcp-server.js Path:

   • Open Command Prompt and navigate to your project directory using cd \path\to\your\project.
   • Run the command: cd (or echo %cd% for the full path)
   • Append \mcp-server.js to the output to get the full path.

• Replace the paths with output from which node and the full path to mcp-server.js.
• The SERVER_NAME env var is used by the getServerName tool.

2. Open Cursor and enable Agent Mode

Once enabled, Cursor will auto-discover the MCP tools based on your mcp.json.

Example Prompts (Cursor Agent Mode)

You can now use prompts like:

• What's the weather in Tokyo?
• Tell me the server name.

Cursor will automatically invoke:

• getWeatherByCity
• getServerName

Code Structure

mcp-server.js

Defines tools and connects to Cursor via StdioServerTransport.

• Tool: getWeatherByCity

  • Input: { city: string }
  • Fetches weather from Express server at localhost:4000/api/weather

• Tool: getServerName

  • Output: Value from process.env.SERVER_NAME

express-api.js

• Route: /api/weather?city=CityName

  • Uses https://wttr.in (no API key needed)
  • Returns { city, temperature, description }

Technologies Used

• @modelcontextprotocol/sdk
• Express
• Zod
• node-fetch
• wttr.in

Optional: Global Cursor Configuration

You can also move the mcp.json file to your global Cursor directory:

~/.cursor/mcp.json

This allows the MCP integration to work across all Cursor projects.

🧰 MCP Server Setup & Tool Configuration Guide

This guide walks through the setup of the mcp-with-express MCP server and how we define tools that plug into Cursor (or other MCP-compatible AI environments).

🚀 MCP Server Initialization

const server = new McpServer({
  name: "mcp-with-express",
  version: "1.0.0",
});

This creates an MCP server instance with a name and version. It’s how Cursor knows what this server is called.

🛠️ Defining Tools with server.tool(...)

The server.tool function is how you expose callable tools (functions) to the AI.

Syntax

server.tool(name, description, inputSchema, handler);

🧪 Example: getServerName

server.tool("getServerName", "Get the server name", {}, async () => ({
  content: [
    { type: "text", text: process.env.SERVER_NAME || "No server name set" },
  ],
}));

• ✅ No input needed
• 📦 Reads SERVER_NAME from environment
• 📤 Returns it as text content

🌦️ Example: getWeatherByCity

server.tool(
  "getWeatherByCity",
  "Get weather by city name",
  { city: z.string() },
  async ({ city }) => {
    const response = await fetch(`http://localhost:4000/api/weather?city=${encodeURIComponent(city)}`)
    ...
  }
)

• ✅ Accepts a city name
• 🔁 Calls your Express API at http://localhost:4000/api/weather
• 📦 Returns a human-friendly weather string

This demonstrates how you can wrap existing APIs in tools — clean separation of tool logic and data retrieval.

🔌 Connecting MCP to Cursor via Stdio

const transport = new StdioServerTransport();
await server.connect(transport);

This tells the MCP server to communicate using standard input/output — the format Cursor understands.

💡 TL;DR

• Define tools with server.tool(...)
• Wrap external or internal APIs in a clean, async interface
• Use Zod for input validation
• Connect with StdioServerTransport for Cursor integration

Happy MCP’ing! 😎

References

• Model Context Protocol Introduction
• MCP TypeScript SDK GitHub
• wttr.in weather API