Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, closed-world, and non-destructive, so the safety profile is fully covered. The description adds genuine value by disclosing the content of the response, including the three-state capability model and the 'what agents may and may not do' policy scope, which matters given there is no 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.