Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description fully discloses the challenge-response behavior, including that signing happens in the user's wallet and not in the tool, and that secrets must never be shared. It also clarifies that the tool returns a challenge rather than completing registration.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.