Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description partially carries the burden. It lists the output fields, giving insight into the result structure. However, it does not disclose behavioral details such as computation assumptions, data currency, or side effects, which are minimal for a calculator.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.