Gauge anomalies on shell and collinear factorization

We revisit gauge anomalies from the purely on-shell perspective. We argue that violation of anomaly cancellation conditions manifests as a breakdown of collinear factorization. We explicitly construct one-loop 5-point amplitudes with graviton exchange displaying singular behavior in collinear limits that cannot be reconciled with factorization theorems. In this approach, gravity serves as a universal probe of both abelian and non-abelian anomalies.