Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (readOnlyHint=false, idempotentHint=false, destructiveHint=false), and the description adds substantial context beyond them: credit consumption triggers, cache-first behavior regardless of age, the 7-day refresh floor with refreshAvailableAt, and the asynchronous 'returns immediately with a report id and status' contract. That is exactly the non-obvious operational behavior an agent needs.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.