Model Context Protocol (MCP) Implementation

This project implements the Model Context Protocol (MCP) for building AI tools. It provides a modular framework that can be used to create MCP-compatible servers and clients.

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🔍 What is Model Context Protocol (MCP)?

The Model Context Protocol (MCP) is an open protocol that enables AI assistants to interact with external tools and data sources.

Key Features

• List available tools and their capabilities
• Call tools with parameters
• Handle errors in a consistent way
• Process tool results in a standardized format

📚 For a detailed overview, see MCP Notes.

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✨ Features

Category	Features
Core	✅ JSON-RPC 2.0 message handling ✅ Protocol initialization ✅ Capability negotiation
Tools	✅ Tool registration with JSON Schema ✅ Tool invocation and validation ✅ Standardized error handling
Transport	✅ STDIO support ✅ HTTP+SSE Support
Testing	✅ Test clients

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📁 Project Structure

src/
├── core/           # Core MCP server implementation
├── transports/     # Transport layer implementations (stdio, HTTP+SSE)
├── tools/          # Tool definitions and handlers
├── examples/       # Example servers and clients
│   └── public/     # Static files for HTTP server
└── index.js        # Main entry point for the library

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🚀 Getting Started

Prerequisites

• Node.js 20.x or later
• npm or pnpm

Installation

# Clone the repository
git clone https://github.com/AshikNesin/learn-mcp-by-building
cd learn-mcp-by-building

# Install dependencies
npm install
# or
pnpm install

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🏃‍♂️ Running the Examples

STDIO Server and Client

Run the STDIO server:

npm run server:stdio
# or
node src/examples/stdio-server.js

Test with the STDIO client:

npm run client:stdio
# or
node src/examples/stdio-client.js

Run both together to see a complete test:

npm run test:stdio
# or
node src/examples/stdio-client.js | node src/examples/stdio-server.js

HTTP+SSE Server and Client

Run the HTTP+SSE server:

npm run server:sse
# or
node src/examples/http-sse-server.js --port 5000

Available options:

• --port: Port to listen on (default: 5000)
• --host: Host to bind to (default: localhost)
• --path: Endpoint path (default: /sse)
• --cors: Enable CORS (default: true)
• --serve-static: Serve static files from src/examples/public (default: true)

Test with the HTTP+SSE client:

npm run client:sse
# or
node src/examples/http-sse-client.js --server http://localhost:5000/sse

Once running, you can also access the web-based client interface in your browser at http://localhost:5000:

The interface provides a user-friendly way to interact with the MCP server, with a side-by-side layout showing the calculator controls and real-time logs.

🔍 Using the MCP Inspector

You can use the official MCP Inspector to debug the server:

npm run debug

The MCP Inspector provides a visual interface for monitoring and debugging MCP servers:

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🧮 Calculator Tool

Operations ➕ add ➖ subtract ✖️ multiply ➗ divide

Parameters operation - Operation type a - First operand b - Second operand

Error Handling Division by zero Invalid operations Type validation Missing parameters

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🧑‍💻 Developing with the MCP Framework

Creating a New Server

import { McpServer } from '../core/index.js';
import { StdioTransport } from '../transports/index.js';
import { calculatorToolDefinition, handleCalculatorTool } from '../tools/index.js';

// Create server instance
const server = new McpServer(
  { name: 'my-server', version: '1.0.0' },
  { capabilities: { tools: { listChanged: true } } }
);

// Register tool handlers
server.setRequestHandler('tools/list', () => ({ tools: [calculatorToolDefinition] }));
server.setRequestHandler('tools/call', async (params) => {
  if (params.name === 'calculator') {
    return handleCalculatorTool(params.arguments);
  }
  throw new Error(`Tool ${params.name} not found`);
});

// Start the server
const transport = new StdioTransport();
server.connect(transport)
  .then(() => console.error('Server ready!'));

Creating a New Tool

1. Create a new file in src/tools/:

// src/tools/my-tool.js
export const myToolDefinition = {
  name: 'my-tool',
  description: 'Description of my tool',
  inputSchema: {
    type: 'object',
    properties: {
      // Define parameters
    },
    required: []
  }
};

export async function handleMyTool(args) {
  // Implement tool logic
  return {
    content: [
      {
        type: 'text',
        text: 'Result from my tool'
      }
    ]
  };
}

2. Export the tool in src/tools/index.js:

export * from './my-tool.js';

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🛠️ Protocol Features

• ✅ Capability negotiation
• ✅ Tool list change notifications
• ✅ Standardized error handling
• ✅ JSON Schema validation
• ✅ Structured tool results
• ✅ Transport layer abstraction

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📚 External Resources

• MCP Protocol Specification
• JSON-RPC 2.0 Specification
• MCP GitHub Repository

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📝 License

MIT