Your first server
What a server actually is
A Model Context Protocol server is not a web server. It is a program that answers questions about what it can do, and then does those things when asked.
A model connects to it, asks what tools exist, reads their descriptions, and decides which to call. That is the whole idea.
Why the description matters
The description is not documentation for a human who will read the source. It is the only thing a model has to go on when choosing between tools.
A tool called multiply with no description is invisible to the thing that is supposed to use it.
What to do
Change the name the server gives itself, then register a tool called multiply that takes two numbers and returns their product as text.
Everything you write runs in a sandbox on its own origin. Press Run and the session appears beside your code, frame by frame.
Written against revision 2026-07-28