Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint annotation, the description discloses that the time series is collapsed into a direction and breakdowns are limited to five items, explaining why raw chart points are not returned. This adds meaningful behavioral context. It doesn't cover pagination or auth, but for a simple read-only analytics tool, this is substantial.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.