Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the read-only, idempotent, non-destructive, closed-world profile, so the description isn't burdened there. It adds real value beyond them by disclosing the entitlement gate ('Tier: sp500+ (sample rejected)') and the caller-scoped, newest-first result ordering, though it does not describe cursor/end-of-list behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.