Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive), but the description adds genuine non-obvious behavior: an anonymous detail view is logged for seller analytics, and unknown ids return an error result with error 'not_found'. Those are traits the annotations cannot express, though it stops short of describing the response payload structure.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.