Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds behavior the annotations cannot: the ~5 minute expiry window after the session was opened and the explicit anti-polling instruction ('not in a loop'), which is real operational context. It stops short of describing the response shape, though an output schema exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.