We describe our experience designing and implementing a highly interactive, online computational tool in Jupyter Notebooks. The lessons learned and subsequent design choices can be applied to similar tools in various domains. This tool, Superpower, is a graphical interface for a set of functions designed to help users to perform power analysis on their study design in psychology. The supported statistical functions are computationally non-trivial in that each power analysis function requires many multidimensional parameters that unavoidably make use of lists or numpy arrays. It is also highly interactive such that user manipulation of any single value or element may require a cascade of updates to others.