Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, so safety is covered; the description adds genuinely useful behavioral context instead of repeating it — the window is always compared against the previous equal-length window, and topics are keyword themes from opening messages rather than a classifier, which warns the agent against over-trusting them. It does not mention pagination or result size limits beyond the schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.