Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnlyHint, idempotentHint, non-destructive and closed-world behavior, so the bar is lowered. The description still adds real value beyond those: it discloses the answer-type aggregation constraint and the authentication requirement (anonymous sessions are told to sign in), which the annotations do not convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.