modelcontextprotocol--python-sdk/docs/handlers/index.md

Inside your handler

A handler's arguments come from the client. Everything else it can read, and everything it can do while it runs, is here.

What it can read:

• The Context is the one extra parameter any handler can ask for: the live request, its headers, its session, and the progress and change-notification verbs.
• Dependencies are parameters the model never sees, filled in by your own functions with Resolve.
• Lifespan covers state your server builds once at startup, and how a handler reaches it through the Context.

What it can do while it runs:

• Ask the user for more input with Elicitation, and Multi-round-trip requests, the 2026-07-28 pattern that carries it.
• Ask the client for an LLM completion or its workspace folders with Sampling and roots, deprecated but still served.
• Report Progress on something slow.
• Write logs (to standard error, for whoever operates the server) with Logging.
• Tell subscribed clients that something changed with Subscriptions.

If you haven't registered a handler yet, start with Tools. Every page here assumes you have one.