Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish non-read-only, non-idempotent, open-world behavior, and the description usefully adds the credit-consumption cost trait that annotations do not cover. It does not disclose what conversion produces, whether it is reversible, or whether it can be re-run without incurring further spend.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.