Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the read-only, idempotent, non-destructive annotations, the description discloses the important behavioral boundaries: the token is a credential that must never be guessed or enumerated, and the response deliberately omits address, phone, and payment details. This is high-value behavioral context that structured annotations alone do not provide.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.