Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations provided, the description carries the behavioral disclosure burden. It discloses the external requirement (own Facebook app), the optional cached-token behavior, and the output type. It could state more about side effects or token expiration, but the key behavioral traits are transparent enough for a non-destructive auth helper.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.