  We discuss the limitations to the use of the effective field theory approach
to study dark matter at the LHC. We introduce and study a few quantities, some
of them independent of the ultraviolet completion of the dark matter theory,
which quantify the error made when using effective operators to describe
processes with very high momentum transfer. Our criteria indicate up to what
cutoff energy scale, and with what precision, the effective description is
valid, depending on the dark matter mass and couplings.
