Does the description disclose side effects, auth requirements, rate limits, or destructive behavior?
Annotations declare this is a non-read-only, non-destructive, non-idempotent write scoped to the local system. The description adds value beyond them by disclosing the auth requirement ('Admins only') and the actual effect (opening a pull request in the connected repository), plus the failure precondition that explains why a retry is needed. It does not explain the non-idempotency consequence (e.g., possible duplicate PRs).
Agents need to know what a tool does to the world before calling it. Descriptions should go beyond structured annotations to explain consequences.