Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only supply readOnlyHint=true; the description adds substantial context the annotation cannot: the meaning of `pending_approval`, the override-vs-account-default resolution, and the per-subtype keying semantics. It even documents the return shape, which matters since no output schema exists.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.