The Alloy Theoretic Automated Toolkit (ATAT) drastically simplifies the practical implementation of the Connolly-Williams method, in combination with semi-grand-canonical Monte Carlo simulations, thus providing a high-level interface to the calculation of thermodynamic properties from first principles. This toolkit enables researcher to focus on higher-level aspects of first-principles thermodynamic calculations by encapsulating the intricate details of the calculations under an easy-to-use interface. It also makes these powerful methodologies readily available to the wide community of researchers who could benefit from it.