Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already mark the tool as read-only, idempotent, and non-destructive. The description adds valuable behavioral nuance via the conditional 'if GPS has one,' indicating the inspection data may not always be present. This goes beyond what annotations alone convey, though it could mention behavior for unknown slugs.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.