Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the full burden, and it does disclose the single externally visible effect: it returns an authorization URL after starting a login process. It omits whether a server-side session or pending-auth state is created, how long the URL/state remains valid, and whether any credentials or config must already exist.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.