Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the burden. It discloses that the estimate is model-based and not billable, which is useful. However, it does not mention whether it modifies state, requires specific authentication, or what happens if inputs are invalid, leaving some transparency gaps.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.