The Exoplanet Characterization ToolKit (ExoCTK) is an open-source, modular, data analysis software package focused primarily on the atmospheric characterization of exoplanets and time-series observation planning. The web application runs the most recently released version of ExoCTK through a web portal designed to provide the most useful tools for observation planning, forward modeling, data reduction, limb darkening, light curve fitting, and retrievals. The full version of ExoCTK is available through GitHub.