Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the behavioral burden, but 'Get' clearly indicates a read-only operation with no side effects, and 'local IP address of this machine' describes the result. It does not discuss edge cases like multiple interfaces or IPv4/IPv6 selection, but for a zero-parameter read-only tool the core behavior is transparent enough.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.