A Python based MCP server calculator tool

Darshan Karanth — Sun, 18 Jan 2026 08:37:25 +0000

Summary
Leverage MCP server python SDK to build a local MCP server.

Requirements
Install python version 3.14+
vscode or any IDE
Claude desktop as MCP Client

Steps
Create project directory and configure python virtual env

mkdir calculator
python -m venv venv
source .venv/Scripts/activate

Install and initialize uv

pip install uv
uv init

Add MCP CLI for the project dependencies

pip install mcp[cli]

Edit the created main.py file with the calculator tool

from mcp.server.fastmcp import FastMCP

# Initialize the MCP server
mcp = FastMCP("Simple Calculator")

@mcp.tool()
def add(a: float, b: float) -> float:
    """Adds two numbers together."""
    return a + b

@mcp.tool()
def subtract(a: float, b: float) -> float:
    """Subtracts b from a."""
    return a - b

@mcp.tool()
def multiply(a: float, b: float) -> float:
    """Multiplies two numbers."""
    return a * b

@mcp.tool()
def divide(a: float, b: float) -> str:
    """Divides a by b. Handles division by zero errors."""
    if b == 0:
        return "Error: Cannot divide by zero."
    return str(a / b)

if __name__ == "__main__":
    mcp.run(transport="stdio")

Install claude code and run the MCP server

uv run mcp install main.py
[01/18/26 13:34:04] INFO     Added server 'Simple Calculator' to Claude config                                                                      claude.py:136
                    INFO     Successfully installed Simple Calculator in Claude app                                                                    cli.py:485
(.venv)

Check File -> Settings -> Developer on claude code if the recently created MCP server is running.

Click Edit config to see the MCP servers configured on the Claude desktop

{
    "mcpServers": {
        "Simple Calculator": {
            "command": "C:\\Users\\MCP\\calculator\\.venv\\Scripts\\uv.EXE",
            "args": [
                "run",
                "--frozen",
                "--with",
                "mcp[cli]",
                "mcp",
                "run",
                "C:\\Users\\MCP\\calculator\\main.py"
            ]
        }
    }
}

Test the MCP server

Start the conversation and provide an arithmetic calculation. Notice that claude leverages the calculator MCP server.
Claude asks for tool access and performs subsequent calculation.

DEV Community: Darshan Karanth

A Python based MCP server calculator tool