Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already flag destructiveHint and idempotency, but the description adds the state machine it operates over (sent, failed, cancelled, in-flight), the refusal code like_not_cancellable with a reason, and the not-found case like_not_found. That is real behavioral context beyond structured fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.