Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive, but the description adds material behavior beyond them: a free sample is returned, the paid URL plus pay steps are included, no charge happens at this call, and the full result costs $17 Base USDC via x402. That payment-flow and cost disclosure is exactly the kind of context an agent needs before invoking.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.