Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover readOnly/idempotent/non-destructive, so the bar is lower, and the description still adds real semantic value: only this record is quotable, draft status is not a commitment, and proposed change orders authorize neither discounts nor extra work. This tells the agent how to interpret returned data, not just that the call is safe.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.