Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, and non-open-world, so the safety profile is covered. The description adds real value beyond that by disclosing the success return shape and the failure behavior (unknown URI returns an error with an `available_uris` list), which is not in the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.