Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnlyHint=true and destructiveHint=false, so the safety profile is covered. The description adds genuine behavioral context beyond that: unauthenticated callers see only a public cutoff, authenticated callers additionally receive their own frozen forecast, and all other forecasts stay private until aggregate scoring. This visibility/auth nuance is valuable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.