Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and non-destructive, lowering the burden. The description adds value by enumerating the exact details returned (what it does, usage, benchmark scores, source repository, URL) and provides an example endpoint, which is useful behavioral context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.