Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, and non-destructive behavior, so the bar is lower. The description adds useful context beyond annotations by revealing that unauthorized related fields are masked, which is a meaningful authorization-dependent behavior. It could go further by explaining what 'unauthorized' means or what errors occur, but it does contribute real contextual value.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.