server.py

#!/usr/bin/env python3
"""
MCP Server - Calculator Tool
Exposes a calculator through Model Context Protocol (MCP)
"""

import asyncio
from mcp.server import Server
from mcp.server.stdio import stdio_server
from mcp.types import Tool, TextContent

# Create MCP server
app = Server("calculator-server")


# Step 1: Define available tools
@app.list_tools()
async def list_tools() -> list[Tool]:
    """Register the calculator tool with its JSON schema"""
    return [
        Tool(
            name="calculator",
            description="Performs arithmetic: add, subtract, multiply, divide",
            inputSchema={
                "type": "object",
                "properties": {
                    "operation": {
                        "type": "string",
                        "enum": ["add", "subtract", "multiply", "divide"],
                        "description": "The operation to perform"
                    },
                    "a": {"type": "number", "description": "First number"},
                    "b": {"type": "number", "description": "Second number"}
                },
                "required": ["operation", "a", "b"]
            }
        )
    ]


# Step 2: Handle tool execution
@app.call_tool()
async def call_tool(name: str, arguments: dict) -> list[TextContent]:
    """Execute the calculator tool and return result"""
    if name != "calculator":
        raise ValueError(f"Unknown tool: {name}")
    
    op = arguments["operation"]
    a = arguments["a"]
    b = arguments["b"]
    
    # Perform the calculation
    if op == "add":
        result = a + b
    elif op == "subtract":
        result = a - b
    elif op == "multiply":
        result = a * b
    elif op == "divide":
        result = a / b if b != 0 else "Error: Division by zero"
    
    return [TextContent(type="text", text=f"{a} {op} {b} = {result}")]


# Step 3: Run the server
async def main():
    async with stdio_server() as (read_stream, write_stream):
        await app.run(read_stream, write_stream, app.create_initialization_options())

if __name__ == "__main__":
    asyncio.run(main())