Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and destructive hints; the description adds useful context beyond them: no account is required, and no execution or posting authority is granted. There is no contradiction with annotations. It does not describe return or pagination behavior, but that is a minor gap for a zero-parameter read-only list.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.