Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, non-destructive, closed-world), so the description's added value is the null-when-absent contract and a sketch of the returned payload (why/impact/steps plus agent prompt). That is meaningful behavior beyond the annotations, though it says nothing about what happens with an invalid productKey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.