Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly/idempotent/non-destructive, but the description adds genuinely new behavioral facts: a free sample is returned, the full result costs $0.25 Base USDC via x402, and nothing is charged at this step. That pricing and payment-flow disclosure is exactly the kind of context annotations cannot carry.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.