Concatenating Calculator MCP Server

# 🔢 Concatenating Calculator MCP Server

An MCP (Model Context Protocol) server that redefines addition — when asked to add two numbers, it concatenates them instead.

📖 Overview

This is a custom Model Context Protocol (MCP) server that exposes an add_numbers tool. Rather than performing arithmetic addition, the tool concatenates the two inputs as strings.

Example:

Input:  add_numbers(3, 5)
Output: "35"

Related MCP server: PyMCP Sum Server

✨ Features

• Implements the MCP server specification

• Exposes a single add_numbers tool

• Concatenates two numbers as strings instead of summing them

• Compatible with any MCP-capable client (e.g. Claude for Desktop)

🚀 Getting Started

Prerequisites

• Node.js v18+ (or your relevant runtime)

• An MCP-compatible client, such as Claude for Desktop

Installation

1. Clone the repository:

   git clone https://github.com/yash312312/custom-mcp-server.git

2. Install dependencies:

   npm install

3. Build the project:

   npm run build

🔧 Configuration

To connect this server to Claude for Desktop, add the following to your claude_desktop_config.json:

{
  "mcpServers": {
    "mcp-server": {
      "command": "node",
      "args": ["/absolute/path/to/your/build/index.js"]
    }
  }
}

💡 Replace /absolute/path/to/your/build/index.js with the actual path on your machine, which is the generated build folder inside the directory.

🛠️ Tool Reference

add_numbers

Concatenates two numbers together as a string.

Returns: A string containing a and b concatenated.

Example:

add_numbers(12, 34)  →  "1234"
add_numbers(0, 7)    →  "07"

📁 Project Structure

.
├── src/
│   └── index.ts        # MCP server entry point
├── build/              # Compiled output
├── package.json
└── README.md

🧪 Running Locally

You can test the server directly without a client:

node build/index.js

The server will start and await MCP-compatible input over stdio.

🤝 Contributing

Contributions, issues, and feature requests are welcome! Feel free to open a GitHub Issue or submit a pull request.

📄 License

This project is licensed under the MIT License.

🙋 Acknowledgements

Built using the Model Context Protocol SDK by Anthropic.