Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and idempotentHint=true, and the description adds real behavioral context: invalid mailboxes are rejected with 422, no charge is incurred, no work runs on them, and a successful lookup costs 10 Zooq credits. This goes beyond what the annotations alone state.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.