Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already convey readOnly, openWorld, idempotent, and non-destructive behavior. The description adds valuable context about the data source (JMA official), the specific alert types covered, the fields returned (level, affected area, summary, issue time), and a disclaimer that it is not a life-safety system, going beyond the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.