Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Beyond the readOnlyHint annotation, the description discloses detailed behavioral expectations: it returns questions with answer keys and explanations, and instructs the agent to act as quizmaster by presenting one question at a time, withholding answers until the user commits, keeping score, and applying the 15/20 pass bar. This is rich, actionable context beyond what annotations provide.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.