Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnly, idempotent, non-destructive, closed-world behavior, so the safety profile is covered. The description adds genuinely non-obvious context: the ref_id is resolved server-side from the affiliate/agent record and must not be requested from the user, and the returned URL must be appended for click attribution. It doesn't discuss failure behavior when no affiliate record exists, which would have made it a 5.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.