Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the read-only, idempotent, non-destructive, closed-world profile. The description adds real behavioral context on top: the exact content returned (rank, evidence, bindings, 25 newest payments) and the failure mode for unranked ids, which an agent needs to interpret an empty response correctly.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.