Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
The description goes beyond the readOnlyHint and destructiveHint annotations by explicitly stating there are no side effects, nothing is booked, the estimate is server-authoritative, it returns amountCents and line items, and it fails under a specific invalid combination of apostille and tier. This is rich, useful behavioral context.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.