We present a web-based mission planning tool for the Ultraviolet Spectrograph (UVS) instruments on NASA’s Europa Clipper and ESA’s JUICE spacecraft. Built with JavaScript and CakePHP 5, the tool allows scientists to plan flyby observations in different instrument modes such as scan, stare, or off to meet science goals and data constraints. The tool supports both Clipper-UVS and JUICE-UVS, accommodating their differences. It features an interactive canvas and drag and drop interface where users create observations, combine them with calibration markers, and visualize the full flyby timeline with fractional second precision alongside spacecraft parameters. The tool employs a queueing system and Docker containers to run external IDL and Python software that generate spectral image outputs and integrates with a separate CakePHP site that provides instrument field of view visualization. This integrated environment helps optimize instrument operations to maximize science return while minimizing data volume and power consumption.