Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, so the safety profile is covered. The description adds genuinely useful behavioral context beyond that: 'A missing receipt means acceptance is uncertain, not that it never ran' — a non-obvious interpretation rule an agent would otherwise get wrong.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.