Detailed studies of exoplanet and brown dwarf atmospheres rely on precise knowledge of the spectral features of possible atmospheric species. These features are a result of the interaction of different molecules and atoms with the radiation of the host star or the intrinsic thermal radiation of the object. The interaction is described by the opacity of a species, which determines how much light is absorbed at a given wavelength. The strength and shape of these opacities are very dependent on the temperature and pressure of the atmosphere, which is why they have to be calculated for a wide range of conditions. line racer is a Python package that enables computing high-resolution opacities from large molecular line lists in an effective manner. It offers users a wide range of options to customize opacity calculations to their needs and available hardware. The code is designed for efficient parallelization on multi-core and multi-node systems and can produce outputs compatible with popular atmospheric modeling and retrieval tools.