Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly=false, destructive=false, non-idempotent, closed-world), so the description needn't repeat that. It adds genuinely new behavioral facts: the operation costs no credits and requires OAuth or a Bearer API key, including where to obtain the key — details absent from all structured fields.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.