Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the full burden. It implicitly states a safe read operation by saying 'list all', and clarifies the content as 'working hours and availability rules'. It does not mention side effects, but for a list operation that is acceptable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.