Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive, and the description adds valuable context beyond them: no quota is consumed, and a successful model listing does NOT prove image-generation permission. That caveat is exactly the kind of behavioral nuance annotations cannot convey. It falls short of 5 because there is no output schema and the description does not say what a result looks like or how to read a failure.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.