RAT is an acronym for Reflectivity Algorithms Toolbox for Rascal. This is a MATLAB toolbox for analysing neutron reflectivity data at multiple contrasts. This is designed to fit multiple contrast neutron reflectivity data, primarily using the Abeles layer model but user-defined model function are also supported. RAT was originally developed by Dr. Arwel Hughes in MATLAB. It is converted to C++/MEX using MATLAB Coder to improve the performance.