Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnly, idempotent, non-destructive and closed-world, so safety is covered. The description adds valuable provenance context beyond that: 'Original bank data free' and 'Not independently verified' are data-quality caveats an agent cannot get from annotations, plus temporal coverage and change-frequency characteristics.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.