Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint, idempotentHint, and non-destructive behavior, so the safety profile is covered. The description adds value by disclosing the scope (every check, or one type) and the shape of the result (current result plus one-line summary).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.