MCP Builder

Create Model Context Protocol (MCP) servers to expose tools and resources to AI agents.

MCP Concepts

• Tools: Functions the AI can call (e.g., search_database, send_email)
• Resources: Data the AI can read (e.g., files, DB records)
• Prompts: Reusable prompt templates

Quick Start (Python)

python
from mcp.server import Server
from mcp.server.stdio import stdio_server
from mcp import types

server = Server("my-server")

@server.list_tools()
async def list_tools() -> list[types.Tool]:
    return [
        types.Tool(
            name="my_tool",
            description="What this tool does and when to use it",
            inputSchema={
                "type": "object",
                "properties": {
                    "param": {"type": "string", "description": "Parameter description"}
                },
                "required": ["param"]
            }
        )
    ]

@server.call_tool()
async def call_tool(name: str, arguments: dict) -> list[types.TextContent]:
    if name == "my_tool":
        result = do_something(arguments["param"])
        return [types.TextContent(type="text", text=str(result))]
    raise ValueError(f"Unknown tool: {name}")

async def main():
    async with stdio_server() as streams:
        await server.run(*streams, server.create_initialization_options())

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

Tool Design Guidelines

• Name: lowercase_underscore, descriptive verb_noun
• Description: Explain what it does AND when the AI should call it
• Parameters: Use JSON Schema; mark required fields; add descriptions
• Returns: Plain text or structured JSON as TextContent

Common Patterns

API wrapper

Wrap REST APIs as MCP tools. Handle auth, rate limits, and error responses gracefully.

File operations

Expose read/write/list operations scoped to a safe directory.

Database queries

Wrap SQL queries with parameterized inputs to prevent injection.

Testing

bash
# Run server directly
python server.py

# Test with MCP inspector
npx @modelcontextprotocol/inspector python server.py