Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint and openWorldHint, so safety is covered. The description adds genuinely non-obvious behavior: a credit cost model (1 credit per record, minimum 2), advice to bound page_size, and the retention rule that only the latest items are kept per app. Missing only return-format detail, which the output schema supplies.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.