Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already cover safety (readOnly, idempotent, non-destructive, open-world), so the description's value-add is the cost model: free within a daily allowance, then $0.003 USDC per call via x402. That is real behavioral context an agent cannot get from the schema. It stops short of stating rate limits or matching semantics.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.