Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, non-destructive behavior. The description adds valuable behavioral context beyond annotations: the 10-credit cost, the 20-result page limit, cursor-based pagination, and the returned first/last name fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.