Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, non-destructive and closed-world, so the safety profile is fully covered. The description contributes the useful fact that results span the funnel (signals through customers) plus credits per reply, but says nothing about how the time window affects the result or whether data is a snapshot vs live.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.