mcp-builder

Build an MCP server using FastMCP (Python) or the MCP SDK (Node/TypeScript) to create tools that expose external service APIs to LLMs. Define tool schemas with Pydantic or Zod validation, implement error handling, and structure responses as JSON or Markdown to enable LLMs to call your services directly.

Design tools with agent-centric principles: provide actionable error messages, minimize token usage, subdivide complex tasks naturally, and use clear input/output schemas. Validate inputs with Pydantic (Python) or Zod (TypeScript) and return structured, truncated responses that guide the LLM toward effective decision-making.

Yes. Build an MCP server that wraps your service's API, define tools for common operations (retrieve records, create leads, update data), and connect it to Claude or another LLM. The MCP protocol handles communication, letting the LLM call your tools as if they were native functions.

No. Choose one: FastMCP for Python or the MCP SDK for Node/TypeScript. Both support the same protocol and capabilities—tool design, validation, error handling, and pagination. Pick based on your existing stack and dependencies.

Create evaluation scenarios with realistic, multi-step questions that require your tools to solve. Test whether the LLM can retrieve data, perform actions, and handle errors correctly. This drives development and surfaces design flaws before production use.

Implement input validation with Pydantic or Zod, enforce character limits with truncation policies, handle external API failures gracefully with clear error messages, and consider authentication scoping. Design tools to fail safely and guide LLMs toward recovery.