Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, non-destructive. Description adds that there is no compute, no rate limit, and it works even if the trigger is closed. It also clarifies `exposure_order` is an ORDER, not a score, and warns against interpreting it as a grade/percentage—valuable behavioral nuance beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.