We present work designed to compute baryon masses on $N_f = 2 + 1$ CLS ensembles including
isospin-breaking effects due to non-degenerate light quark masses and electromagnetic interactions.
These effects are determined at leading order via a perturbative expansion around the iso-symmetric
theory. We furthermore apply a group-theoretical operator construction for the various interpolators
describing the different members of the baryon octet and decuplet based on a classification by spin,
parity, and flavor content.