Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
With no annotations, the description carries the transparency burden. It discloses that the key set is public and explicitly states 'No private JWK fields are exposed', which is a useful safety guarantee. It doesn't describe pagination or errors, but for a simple key retrieval tool this is adequate.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.