Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the annotations, the description reveals the default behavior (read), the optional unread mode, and the API-key requirement. This supplements the structured hints without contradicting them, though it does not describe response or side-effect details (covered by output schema/annotations).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.