  We introduce a generic and accessible implementation of an exact
diagonalization method for studying few-fermion models. Our aim is to provide a
testbed for the newcomers to the field as well as a stepping stone for trying
out novel optimizations and approximations. This userguide consists of a
description of the algorithm, and several examples in varying orders of
sophistication. In particular, we exemplify our routine using an
effective-interaction approach that fixes the low-energy physics. We benchmark
this approach against the existing data, and show that it is able to deliver
state-of-the-art numerical results at a significantly reduced computational
cost.
