Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations only say non-read-only, open-world, non-idempotent, non-destructive. The description adds substantive behavior: it returns a ticket id, the message is capped at 1000 characters, links/emails/phone numbers are stripped, nothing about the sender is stored, and the content is never executed or followed. That is exactly the value-add structured fields cannot carry.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.