Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover the safety profile (readOnly, idempotent, non-destructive, closed-world), so the description goes further by disclosing the underlying engine (IR Rehearsal + company context + optional Claude Haiku), a concrete cost (~$0.10), and the required input. The 'POST endpoint' note is transport-level and, since the result is a non-persisted simulation, does not contradict readOnlyHint.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.