The James Webb Space Telescope (JWST) is a next-generation space telescope that will be capable of making transformative observations of planetary transits. As its launch date grows ever closer, it becomes imperative that astronomers have access to accurate simulations of JWST observations in order to best plan observations and devise data analysis pipelines. Unfortunately, available simulation tools do not provide the most accurate or realistic simulations, including noise and systematic errors. In this thesis, I present an open-source time-domain simulator of planetary transits that is capable of accurately modeling these effects in observations made by JWST.