Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, and closed-world behavior, so the safety profile is covered. The description adds genuinely new context beyond that: a 1-credit cost, determinism, a 'real parser' implementation, and the two possible outcomes including error text.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.