Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations already declare readOnlyHint=true and idempotentHint=true, so the description doesn't need to cover safety. It adds value by disclosing the output structure (authenticated, pending, connect_url) and the conditional behavior, which is not present in annotations. This exceeds the baseline for annotated tools.
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.