Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive/non-open-world, so the safety profile is covered. The description adds genuinely useful non-schema context: results are for lookup purposes only, copyright vests with the issuing body, and the source URL must be cited — constraints an agent would otherwise not know.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.