Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate write operation (readOnlyHint=false), idempotent (idempotentHint=true), non-destructive. The description adds context by specifying the verification checks (object, content signature, session, expiry, version) and the subsequent record creation, which goes beyond annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.