Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as read-only, non-destructive, idempotent, and open-world. The description adds behavioral details beyond the annotations: the exact time range, default value, and the row-level structure of the response (including lat/lon, parameter, and value). It stops short of discussing rate limits or pagination, but the added context is valuable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.