Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations indicate the tool is read-only, non-destructive, and idempotent. The description adds behavioral context beyond annotations by detailing what the tool returns (confidence scores, alternative formats, unparseable lines, custom patterns). No contradictions.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.