Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, non-destructive, and closed-world. The description adds value beyond these by disclosing the cost ('costs 1 unit'), the consent prerequisite for personal frameworks, and the exact interaction protocol (one question at a time, A/B only). It does not cover rate limits or error behavior, but the added context is substantial.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.