Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description must fully disclose behavior. It only states the calculation, omitting important details such as input constraints (e.g., equal-length numeric arrays), potential errors from non-numeric data, or output format. The existence of an output schema reduces the burden, but the description should still hint at expected behavior.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.