Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already signal read-only, idempotent, and non-destructive behavior. The description adds valuable behavioral context beyond annotations: API key requirement, default unread-only behavior, empty results for new accounts, and the meaning of the message field. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.