Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and idempotentHint=true, so the safety profile is known. The description adds valuable behavioral detail beyond annotations: the comparison window (7 vs 23 days), specific thresholds for 'moderate' and 'significant', and the 'unknown' case for new publishers. This enriches the agent's understanding of expected behavior and edge cases.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.