  We study $4d$ $\mathcal{N}=1$ gauge theories engineered via D-branes at
orientifolds of toric singularities, where gauge anomalies are cancelled
without the introduction of non-compact flavor branes. Using dimer model
techniques, we derive geometric criteria for establishing whether a given
singularity can admit anomaly-free D-brane configurations purely based on its
toric data and the type of orientifold projection. Our results therefore extend
the dictionary between geometric properties of singularities and physical
properties of the corresponding gauge theories.
