Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description adds meaningful behavior beyond the read-only and idempotent annotations: it discloses best-first ranking, returned fields (matched terms, cost, auth, reliability), and the semantic matching behavior that ignores filler words and proper names. This enriches the agent's understanding of call outcomes without contradicting 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.