Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish read-only and non-destructive behavior. The description adds meaningful output-contract transparency by stating the estimate is authorized, singular, field-bounded, and that addresses, notes, and terms are excluded. This goes beyond the annotations by telling the agent what it will and will not receive.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.