Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the tool as read-only, idempotent, and non-destructive, covering safety. The description adds the core output behavior (distinct values and counts) but does not disclose potential limitations like pagination, ordering, or count accuracy.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.