Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare the tool is read-only and idempotent; the description adds that routing is free, requires no payment, and returns schema plus x402 preflight next step. This is useful behavioral context beyond the structured annotations and matches the read-only, non-destructive profile.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.