Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the disclosure burden. It reveals exactly what data the call returns and signals a read-only, side-effect-free operation via 'Read this.' It does not describe the return format, but for a zero-parameter metadata lookup that is a minor gap.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.