Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations provide safety profile (not read-only, not destructive, not idempotent). The description adds behavioral context: monitors keep running, alerts are suppressed, and the window is one-time. This goes beyond annotations and clarifies the tool's effect.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.