  The use of 3D hydrodynamical simulations of stellar surface convection for
model atmospheres is computationally expensive. Although these models have been
available for quite some time, their use is limited because of the lack of
extensive grids of simulations and associated spectra. Our goal is to provide a
method to interpolate spectra that can be applied to both 1D and 3D models, and
implement it in a code available to the community. This tool will enable the
routine use of 3D model atmospheres in the analysis of stellar spectra.} We
have developed a code that makes use of radial basis functions to interpolate
the spectra included in the CIFIST grid of 84 three-dimensional model
atmospheres. Spectral synthesis on the hydrodynamical simulations was
previously performed with the code ASS$\epsilon$T. We make a tool for the
interpolation of 3D spectra available to the community. The code provides
interpolated spectra and interpolation errors for a given wavelength interval,
and a combination of effective temperature, surface gravity, and metallicity.
In addition, it optionally provides graphical representations of the RMS and
mean ratio between 1D and 3D spectra, and maps of the errors in the
interpolated spectra across the parameter space.
