Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare read-only, idempotent, and non-destructive behavior. The description adds value by specifying the data type (account/API-quota metadata) and tying it to the X-API-Key, which gives agents a better mental model of what the response will contain without relying solely on the output schema.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.