Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as readOnly, idempotent, and non-destructive. The description adds useful behavioral detail beyond those hints: the current tariff values, the input format, and the fact that it returns both the total points and the number of grades counted. This is sufficient for a simple calculator.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.