Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations include readOnlyHint=true and openWorldHint=true, establishing the read-only nature. The description adds behavioral details such as validation and the specific return fields (country, carrier, line type, E.164 format), which goes beyond annotations. It does not disclose error handling or format limitations, but the annotations already cover the safety profile.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.