Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden. 'List' clearly implies a read-only operation, and the mention of 'users/system users' adds specificity about what is returned. However, it does not disclose authentication requirements, response shape, pagination, or whether system users require special permissions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.