  In this study we present a universal effective action for one-loop matching
of all scalar leptoquarks. We use both the Universal One-Loop Effective Action
(UOLEA) and covariant diagrams to evaluate the Wilson coefficients directly in
the Green basis for up-to dimension-6 operators. On the technical side, we use
the newly developed method of evaluating supertraces, to further validate the
results stemming from the use of covariant diagrams. As an application, we
perform a fully functional matching onto Standard Model Effective Field Theory
(SMEFT) of a model with two scalar leptoquark fields: a weak isospin singlet
and a doublet. We demonstrate its use by calculating several observables, such
as lepton magnetic and electric dipole moments, neutrino masses, proton decay
rate, while we comment upon fine tuning issues in this model. Apart from its
phenomenological interest, this model generates the majority of dimension-6
operators and provides an EFT benchmark towards future matching automation.
