Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive and closed-world, so the safety profile is covered. The description adds genuinely new behavioral context beyond them: it discloses that results are historical-only and do not imply availability, and it names privacy exclusions (broker contact details, account identifiers), which matters for downstream use of the data. It stops short of describing result shape or whether the list is paged.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.