🟢 MCP Server in Node.js

Build and run a custom MCP Server in Node.js in just 2 minutes ⏱️

Overview · Features · Installation · Testing with MCP Inspector · Setting Environment Variables for Testing · Integrating with Cursor AI · Using the MCP Tool in Cursor (Agent Mode) · Code Overview · References & Resources · License

Overview

MCP (Model Context Protocol) is a framework that allows you to integrate custom tools into AI-assisted development environments—such as Cursor AI. MCP servers expose functionality (like data retrieval or code analysis) so that an LLM-based IDE can call these tools on demand. Learn more about MCP in the Model Context Protocol Introduction.

This project demonstrates an MCP server implemented in JavaScript using Node.js. It defines two tools: add, which takes two numeric inputs and returns their sum, and getApiKey, which retrieves the API key from the API_KEY environment variable. It also provides a predefined prompt add_numbers that allows AI models to infer the usage of the addition tool.

Requirements

• Node.js: Version 20 or higher is required.

Features

• MCP Integration: Exposes tool functionality to LLM-based IDEs.
• Addition Tool: Accepts two numeric parameters and returns their sum.
• MCP Prompt: Provides a predefined prompt ("add_numbers") that allow AI models to infer tool usage.
• Env Var Retrieval: Demonstrates how to load an example environment variable from the configuration file.
• Input Validation: Uses Zod for schema validation.
• Standard I/O Transport: Connects via StdioServerTransport for integration with development environments.

Installation

1. Clone the Repository

   git clone <repository_url>
   cd <repository_directory>
   

2. Install Dependencies

   You can install the project dependencies in one of two ways:

   Option 1: Install using the existing package.json

   Simply run:

   npm install
   

   Option 2: Install dependencies manually

   If you prefer, delete the existing package.json and install the required packages manually:

   npm install @modelcontextprotocol/sdk zod
   

   Then, update the newly generated package.json file to include the following lines, which enables ES Modules and adds the mcp inspector command:

   "type": "module",
   "scripts": {
    "inspector": "npx @modelcontextprotocol/inspector node ./mcp-server.js"
   }
   

Testing with MCP Inspector

The MCP Inspector is a debugging tool that lets you test your server's tools interactively before integrating with an IDE.

Option 1: Run directly with npx

npx @modelcontextprotocol/inspector node ./mcp-server.js

Option 2: Use the npm script

npm run inspector

This will:

1. Start the MCP inspector server
2. Open your browser to the inspector interface
3. Allow you to test tools, resources, and prompts

Open the MCP Server Inspector on the browser: http://localhost:6274/

Setting Environment Variables for Testing

To test the getApiKey tool with different API keys, you can set environment variables before running the inspector:

Linux/macOS (Bash/Zsh):

# Temporary (current session only)
export API_KEY="your-test-key"
npm run inspector

# Or set for single command
API_KEY="your-test-key" npm run inspector

Windows (Command Prompt):

# Set for current session
set API_KEY=your-test-key
npm run inspector

Windows (PowerShell):

... [View full README on GitHub](https://github.com/lucianoayres/mcp-server-node#readme)