Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations cover the safety profile (readOnly, idempotent, non-destructive), so the bar is lower. The description adds the important constraint that history is bounded by retention and storage and is not an unlimited audit log, which is genuinely useful behavioral context. It doesn't disclose pagination behavior or ordering, which would help more.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.