Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and destructiveHint=false. The description adds meaningful context beyond that: it is a reference lookup with no purchase-gate side effects, and it notes the eSIM works in all 193 countries. It doesn't discuss return format or errors, but the output schema covers that.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.