Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the read-only/idempotent annotations, the description discloses meaningful data semantics: empty markets, brandVoice, or photographyGuidelines inherit the brand's values, empty ageRange/gender/language means any, and results truncate beyond limit. This adds real interpretive context for the returned audiences.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.