Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish the operation is read-only, idempotent, and non-destructive, so the description carries a light burden. It adds value by specifying the return composition (active/upcoming/past seasons and per-challenge progress), which is especially helpful because no output schema is provided.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.