JFDTD is an on-line Maxwell's equations solver based on the finite difference time domain method. It handles one, two, or three dimensions. A variety of boundary types are available for terminating the simulated volume. A variety of sources are also available, including a total field scattered field (TFSF) planewave source. Inputs and outputs are stored in a MySQL database by user name and project name. Projects are run on a dedicated server in batch mode using a first-in first-out queue. The queue is updated every half hour by scanning the database for new projects. For a detailed description of the web-based user interface, please see the JFDTD wiki.