Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark it read-only, idempotent, and non-destructive. The description adds meaningful behavioral context: credit cost, slug-to-id resolution cost behavior, and that data.activities[].entityId feeds /posts/info, /posts/comments, /posts/likes. No contradiction with annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.