RefractiveIndexTools is a handy app that brings together useful calculators and plots for studying how light and materials interact. You can find special angles like the Brewster angle or the critical angle, see how much light is reflected at different angles, and quickly solve Snell’s Law for refraction. The app also helps predict thin film colors, compare refractive indices between media, and check material stiffness from stress–strain data. Beyond optics, it offers easy tools for fluid pressure, seepage flow in soils, and angle of repose for granular piles. Whether you’re working on coatings, fiber optics, sensors, or engineering designs, this app provides quick answers with simple steps, saving you time and effort.