Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover safety (readOnly, idempotent, non-destructive), but the description adds material behavior beyond them: the call returns only a free sample plus a paid URL and pay steps, no charge is incurred here, and the full result costs $0.02 Base USDC via x402. That payment/partial-result behavior is exactly what an agent needs and cannot infer from annotations.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.