Demo 01

A local MCP (Model Context Protocol) server for Claude Desktop.

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Table of Contents

• Overview
• Project Structure
• Getting Started
  • Prerequisites
  • 1. Clone the Repository
  • 2. Install Dependencies
  • 3. Configure Claude Desktop
  • 4. Restart Claude Desktop
  • 5. Verify the Setup
• How the Server Starts
• How It Works — End-to-End Flow
• Tool Reference
• Troubleshooting

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Overview

This project is a local MCP (Model Context Protocol) server that extends Claude Desktop with custom tools. MCP is an open protocol that allows Claude to interact with local services, files, APIs, and more — turning Claude into a powerful assistant tailored to your specific workflow.

This server is built with the MCP TypeScript SDK and runs locally on your machine via stdio transport. Once configured, Claude Desktop automatically starts the server and makes its tools available in every conversation.

What's included

• calculate — Performs basic math operations: add, subtract, multiply, and divide

This is a starter project — you can easily extend it by adding more tools in src/index.js.

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📁 Project Structure

demo-mcp-01/
│
├── src/
│   └── index.js          # MCP server entry point
│
├── tools/
│   └── calculate.js      # Calculate tool logic
│
├── .gitignore            # Ignore node_modules, .env, etc.
├── package.json          # Dependencies and scripts
└── README.md             # This file

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Getting Started

Prerequisites

• Node.js v18+
• Claude Desktop

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1. Clone the Repository

git clone https://github.com/santanu2908/demo-mcp-01.git
cd demo-mcp-01

2. Install Dependencies

npm install

3. Configure Claude Desktop

Create a file named claude_desktop_config.json in the Claude config folder.

Config folder path (Windows):

C:\Users\<YourUsername>\AppData\Roaming\Claude\

💡 To quickly open this folder, press Win + R and type: %APPDATA%\Claude If the Claude folder doesn't exist, create it manually.

Paste the following into claude_desktop_config.json, updating the path to match where you cloned the repo:

{
  "mcpServers": {
    "my-local-server": {
      "command": "node",
      "args": [
        "C:\\Users\\<YourUsername>\\path\\to\\demo-mcp-01\\src\\index.js"
      ]
    }
  }
}

⚠️ On Windows, use double backslashes \\ in the path. Example: "C:\\Users\\John\\Documents\\demo-mcp-01\\src\\index.js"

4. Restart Claude Desktop

Fully quit Claude Desktop (check the system tray → right-click → Quit) and reopen it.

5. Verify the Setup

Open Claude Desktop and go to Settings → Developer. You should see my-local-server listed with a green status indicator showing it is running. If it shows an error or is missing, revisit the config path and restart Claude Desktop.

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⚙️ How the Server Starts — No npm start Needed

You never need to manually run npm start or keep a terminal open. Claude Desktop launches the server for you automatically.

When Claude Desktop reads your config:

{
  "command": "node",
  "args": ["C:\\...\\src\\index.js"]
}

It runs node src/index.js as a child process in the background every time Claude Desktop opens. When you close Claude Desktop, it shuts the process down too.

This works because the server uses StdioServerTransport — it communicates via stdin/stdout rather than HTTP or a network port. Claude Desktop pipes messages directly to the process, so there is nothing to manually start or keep alive. Claude Desktop owns the entire process lifecycle.

	Traditional Server	MCP stdio Server
Who starts it?	You (npm start)	Claude Desktop
How does it communicate?	HTTP / WebSocket	stdin / stdout
Who keeps it alive?	You	Claude Desktop
Port needed?	Yes	No

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🔄 How It Works — End-to-End Flow

Here's a walkthrough of a real tool call: "Multiply 12 by 7"

Step 1 — User Prompt

The user sends a message to Claude Desktop:

Use the calculate tool to multiply 12 by 7

Step 2 — Tool Discovery

• Claude used the internal tool_search mechanism to locate the calculate tool by querying "math multiply".
• The tool schema was returned with the following parameters:
  • a → number (first operand)
  • b → number (second operand)
  • operation → one of add | subtract | multiply | divide

Step 3 — Tool Invocation

• Claude called the calculate tool with:

  a = 12
  b = 7
  operation = multiply
  

• The server executed the operation and returned:

  Result: 84
  

Step 4 — Result Verification

• Claude received 84 from the tool and confirmed it as correct.
• This validated the full MCP loop: Claude → Tool Call → Local Server → Result → Claude.

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🛠 Tool Reference

calculate

Performs a basic arithmetic operation on two numbers.

Parameter	Type	Required	Values
a	number	✅	Any numeric value
b	number	✅	Any numeric value
operation	string	✅	add, subtract, multiply, divide

Example Request:

{
  "a": 12,
  "b": 7,
  "operation": "multiply"
}

Example Response:

Result: 84

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Troubleshooting

No hammer icon showing?

• Double-check the path in your config file points to the correct index.js
• Validate your JSON at jsonlint.com
• Make sure Node.js is installed: run node --version in a terminal
• Fully quit Claude Desktop from the system tray before restarting

Config not loading?

• Confirm the file is named exactly claude_desktop_config.json (not .json.txt)
• Confirm it lives in %APPDATA%\Claude\, not inside the project folder

📌 Key Takeaways

• MCP lets Claude call real, external code — not guess answers.
• The calculate tool is deterministic: same input always yields the same output.
• This pattern scales to databases, APIs, file systems, and hardware.

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Built with Model Context Protocol · Connected via Claude.ai Developer Tools