The 1D radiative-convective code PCM_LBL simulates the climates of diverse planetary atmospheres. The code is written in modular modern Fortran and uses a 'brute-force' spectral approach where absorption coefficients are computed on a fixed spectral grid directly from line data. This allows climate calculations to be performed more simply and at higher accuracy than in a correlated-k approach. PCM_LBL allows the user to iterate rapidly between fast, lower accuracy calculations and slow high accuracy calculations. By default, the model is set up to run fairly fast at moderate resolution; the accuracy of the code can be adjusted with a few (documented) changes.