Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish the safe-read profile (readOnlyHint, idempotentHint, non-destructive, closed-world), so the bar is lower. The description adds genuinely new context: the call is free, and there is a boolean done field to poll against, both of which tell the agent how to behave.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.