Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so safety is covered. The description still adds genuine context the annotations cannot: the 3-install agreement rule for facts, the 'no copied quest text' constraint, the Everloot player-data dependency when connected, and explicit reporting of missing data. It stops short of describing paging or partial-result shape, but that is largely covered by the output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.