Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover read-only, idempotent, and non-destructive behavior. The description adds important behavioral traits: it returns only a histogram, not individual classifications, and it counts uncertain items via the confidence threshold. This complements rather than repeats the annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.