Natural or anthropogenic activities can cause a perturbation in Earth's radiative energy budget known as a radiative forcing, which induces a climate response. Diagnosing radiative forcing and its uncertainty is foundational to understanding past and future climate change. Here we outline the protocol for the second iteration of the Radiative Forcing Model Intercomparison Project (RFMIP2.0), which provides a standardized method for diagnosing radiative forcing across Global Climate Models.