  We present an efficient algorithm for determining the Hilbert series of an
effective theory and provide a companion code called ECO (Efficient Counting of
Operators) in FORM. For example, the Hilbert series for the dimension 15
operators in the Standard Model Effective Theory (SMEFT) can be obtained in a
minute on a single CPU core. While our implementation focusses on SMEFT, we
allow for a flexible user input of the light degrees of freedom. Furthermore,
gravity, as well as additional U(1) global or gauge symmetries can be included.
