Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, openWorld, and destructiveHint false. The description adds value beyond annotations by disclosing per-call cost and the 404-billed / 503-not-billed semantics, which an agent needs to reason about cost and retry behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.