Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, and closed-world, so safety is covered. The description adds genuinely new operational context the annotations cannot express: the call costs 1 unit. It doesn't discuss pagination, but the cost disclosure plus the returned-fields hint ('score and the context') is real added value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.