In this paper we describe the semi-spectral linear MHD (SLiM) code which we have written to follow the interaction of linear waves through an inhomogeneous three-dimensional solar atmosphere. The background model allows almost arbitrary perturbations
of density, temperature, sound speed as well as magnetic and velocity fields. We give details of several of the tests we have used to check the code. The code will be useful in understanding the helioseismic signatures of various solar features, including sunspots.
