Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The annotations already declare readOnly, openWorld, idempotent, and non-destructive behavior. The description adds valuable behavioral context beyond that: the error case when neither parameter is supplied, the precedence rule, the return shape, and the 5000-character limit.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.