Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already establish readOnly, idempotent, and non-destructive behavior. The description adds a valuable behavioral detail beyond annotations: on not-found it returns a list of available slugs to help the caller choose the correct one. This enriches the agent's understanding of the tool's failure mode.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.