Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive, openWorld), so the bar is lower. The description still adds real value beyond them: it discloses that the result comes back in two forms (decimals-adjusted and raw) and pins the chain to Base, plus the address literal format.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.