Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds critical behavioral context beyond the annotations: concurrency, non-blocking failure, and the structure of the response (summary + per-item results). Annotations are minimal (readOnlyHint=false, etc.), so the description fully shoulders the transparency burden.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.