Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare idempotentHint=true and destructiveHint=false, but the description adds substance beyond them: it names exactly what is materialised (ExamPaper, questions, mark schemes) and that the operation is synchronous. It also explains the concrete idempotency behaviour (returning the already-committed paper's id), which the hint alone does not convey.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.