Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations and no output schema, the description carries the behavioral transparency burden, and it does disclose the exact contents of the returned field information: key, label, type, required flag, help text, and allowed options. It could be more explicit about being read-only, but the nature of a field-listing tool makes that reasonably inferable.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.