MCP Server in Node.js

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 built in Node.js that provides two basic tools. One tool, add, accepts two numbers and returns their sum, while the other, getApiKey, retrieves the API key from the environment (via the API_KEY variable).

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.
• 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 @coinpaprika/api-nodejs-client zod

   Then, update the newly generated package.json file to include the following line, which enables ES Modules:

   "type": "module"

Integrating with Cursor AI

This project includes a ./cursor subdirectory that contains an mcp.json file for configuring the MCP server. Cursor AI uses this file to automatically discover and launch your MCP server. Open the file and update the fields as follows:

The ./cursor/mcp.json Structure

Below is the full JSON structure of the configuration file:

{
  "mcpServers": {
    "MCP Server Boilerplate": {
      "command": "/path/to/node",
      "args": ["/path/to/mcp-server.js"],
      "env": {
        "API_KEY": "abc-1234567890"
      }
    }
  }
}

• mcpServers:
  An object mapping server names to their configuration.

• MCP Server Boilerplate:
  This is the key for your server configuration. You can name it as you like.

• command:
  Specifies the absolute path to your Node.js executable. For example:

  /home/john/.nvm/versions/node/v20.13.1/bin/node
  

• args:
  An array containing the absolute path to your MCP server file. For example:

  ["/home/john/mcp-server-node/index.js"]
  

• env: (Optional)
  Defines environment variables for your MCP server process. In this example, the API_KEY is set to "abc-1234567890". Adjust this value as needed for your environment.

You can verify the absolute path to your Node.js executable by running which node in your terminal.

Optional: Configuration Automation Scripts

Easily configure your local environment by automatically updating the mcp.json file with the correct absolute paths. To apply your local settings, run the following commands from your project root:

chmod +x ./scripts/update_config.sh
./scripts/update_config.sh

This script replaces the placeholder paths in mcp.json with your machine’s absolute paths for Python and the server script, ensuring your configuration settings are always accurate.

Optional: Global Cursor settings

You can also move the mcp.json file to your global Cursor AI configuration directory located at ~/.cursor to make the configuration available globally.

Using the MCP Tool in Cursor Composer (Agent Mode)

With the MCP server integrated into Cursor AI and with Agent mode enabled in Cursor Composer, simply use a natural language prompt like:

add 3 and 5

or

what is my API key?

The AI agent will infer the available add or getApiKey tool from your MCP server and execute it accordingly.

Code Overview

The project comprises the following key parts:

• MCP Server Initialization:
  The MCP server is instantiated using McpServer from the MCP SDK and connected via StdioServerTransport.

• Tool Definitions:

  • add:
    Defined with a Zod schema that accepts two numbers (a and b) and returns their sum as text.
  • getApiKey:
    Retrieves the API key from the environment variable API_KEY and returns it as text.

What is MCP?

Model Context Protocol (MCP) provides a standardized approach to integrate custom tools into AI-assisted development environments. With MCP, you can define tools that perform specific tasks—such as retrieving external data, validating code, or enforcing coding standards—and the AI assistant in your IDE can call these tools automatically based on context. This helps improve developer productivity, ensures consistent quality, and streamlines workflows.

References & Resources

• Model Context Protocol: typescript-sdk
• Use Your Own MCP on Cursor in 5 Minutes
• Model Context Protocol Introduction

License

This project is licensed under the MIT License.