Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, destructiveHint=false and openWorldHint=false, so 'Free; changes nothing' is largely redundant. The description does add value beyond them by disclosing the required permission scope ('Needs read:library') and the notion of an 'original app-native' receipt, which annotations cannot express. It does not describe what a missing receipt means or what the returned record looks like.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.