McFine performs complex, multi-component hyperfine spectra fitting in astronomical data. It turns line intensities into gas conditions using a fully automated Bayesian method. Written in Python, the code uses Markov chain Monte Carlo (MCMC) to characterize model denegeracies. It handles local thermodynamic equilibrium (LTE) and radiative-transfer (RT) models and can fit individual spectra and data cubes; given a data cube, it can also use the neighboring information to attempt a better fit. McFine also fits the minimum number of distinct components to avoid overfitting.