Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as read-only, idempotent, and non-destructive, so the description adds useful behavioral context rather than replacing the annotations. It adds that content is normalized to readable text and that comparison uses a baseline, plus the per-check cost of $0.03.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.