Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, closed-world), so the description's value is in the semantics it adds: a fixed 14 UTC-calendar-day window, that figures are request counts rather than people or verified agents, and that labeled test traffic is excluded. These caveats materially change how an agent interprets the numbers; only the aggregation/return shape is left unstated.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.