  We present DECO ("Discrete and Efficient Counting of Operators"), an
implementation of the Hilbert Series to enumerate subleading operator bases for
SMEFT-like EFTs with symmetry groups as typically found in flavour and BSM
physics. DECO can accommodate EFTs with arbitrary numbers and combinations of
the SM gauge groups, as well as the discrete groups S4, A4, and Zn, and U(1)
groups with residual global charge (and these groups' most important
representations). The program is highly modular and can easily be extended to
additional groups and/or representations. We demonstrate the design cases for
DECO by using it to cross-check subleading operator bases of EFTs in the
literature, which allows us to identify a missing operator in a widely used
model for the neutrino masses and discuss said operator's impact.
