Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the read-only annotation, the description discloses important behavior: returned changes include deletions, results are oldest-first, the cursor must be persisted, and an entry in the cursor's own second may reappear, requiring deduplication by id. This is valuable operational context not otherwise visible.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.