Calculator MCP Server

A Model Context Protocol server exposing calculator operations, built as a learning project.

Tools

• add(a, b)

• subtract(a, b)

• multiply(a, b)

• divide(a, b)

• power(base, exponent)

• square_root(number)

• modulus(a, b)

Run

uv run mcp dev src/calculator_mcp/server.py

Test

uv run pytest tests/ -v

Architecture

• operations.py — pure calculator logic, no MCP dependency

• server.py — FastMCP tool registration, thin wrappers over operations.py

• exceptions.py — custom exception hierarchy (CalculatorError base)

• tests/ — pytest unit tests, independent of the MCP layer

Connect to Claude Desktop

Add this to claude_desktop_config.json:

{
  "mcpServers": {
    "calculator": {
      "command": "uv",
      "args": ["run", "--directory", "/path/to/calculator-mcp-server", "mcp", "run", "src/calculator_mcp/server.py"]
    }
  }
}

This structure generalizes to any MCP server: keep domain logic separate from protocol code, use typed exceptions per failure mode, annotate tools honestly (readOnly/idempotent/destructive/openWorld), and test the logic layer without needing a live server.