Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover safety (readOnlyHint, idempotentHint, non-destructive), so the description adds useful behavioral context: default scope, newest-first ordering, and the fields returned in each item. This goes beyond the structured data and gives the agent a concrete expectation of the result.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.