Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full behavioral burden and discloses almost nothing: it doesn't say whether the counterparty is notified, whether the request is destroyed or just declined, or what state the caller must be in. 'Reject' implies a state change but no consequences are described.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.