AI Agent MCP Tool Development 2026
Write an MCP weather tool agents can call: full FastMCP code with a free API, testing workflow, and common pitfalls.
💡 What You Will Learn
Write an MCP weather tool agents can call: full FastMCP code with a free API, testing workflow, and common pitfalls.
MCP (Model Context Protocol) is Anthropic's open standard for giving AI agents tools. Once you declare a tool, agents call it automatically - no prompt engineering, no orchestration. This tutorial builds a weather tool with FastMCP and Open-Meteo (free, no API key). Steps: pip install "mcp[cli]" fastmcp; write a FastMCP app with one @mcp.tool function that geocodes a city name then fetches current weather; run with "mcp dev weather.py" to test; register it in Claude Desktop's mcpServers config (command: python, args: [path]). Key design points: write a clear docstring (the LLM decides when to call based on it), return structured errors like {"error": ...} instead of crashing, and set timeouts on external calls. Tools/resources/prompts are the three MCP concepts; tools are the easiest to start with. MCP also supports remote HTTP/SSE connections for server deployment. Check official docs as the spec evolves.
Written by our editorial team; tools listed here are tested or verified against public sources. Links point to official sites or GitHub repos for reference only โ no paid placements.
