Build a tiny server

Build-along · ~15 min at your own keyboard

The final demystification: an MCP server is a small program that announces some tools. Have Claude build you one with two or three tools around YOUR thing — your price list, your service areas, your FAQ — and the whole protocol stops being magic forever.

The long version: Building a tiny MCP server ↗

Mac: Mac: run the server with python3 or node from Terminal and use full paths in .mcp.json.

Windows: Windows: use full paths with doubled backslashes or forward slashes in .mcp.json. Run from PowerShell.

Do this

0/5

Checkpoints

▸You should now see your server's tool list in the code.
▸You should now see it connected after /mcp, and a tool call in the transcript.
▸You should now see a clear result or error for all four test cases.

The three ways this goes wrong

The server does not start. — Ask Claude to run the start command by hand and show you the error.
It connects but the tools are missing. — Check the tool names and schemas in the code and restart the session.
Answers are wrong or empty. — Check the path to your data file is absolute and the file has the fields the tool reads.

Share what happened

Paste your server's tool list, the /mcp confirmation, the tool-call line from the transcript for one answer, and the result of the four test cases.

Strip API keys, passwords, and tokens before you paste. Swap them for [KEY].

🔒 Don't paste confidential, personal-health, or payment info.