Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent and closed-world behavior, and the description still adds real context: the data is drawn from published exam rubrics, the result flags where a per-criterion breakdown is the provider's own, and no sign-in is needed. It stops short of describing result shape, but an output schema exists so that burden is lifted.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.