Magnetism 3D Lab is a free, browser-based interactive magnetic-field simulator for high-school and introductory undergraduate physics. Students construct scenes from straight and finite wires, current loops, solenoids, toroids, bar magnets, and uniform-field regions, then explore the resulting fields in 2D and 3D. Visualization modes include heatmaps, Linear Integral Convolution (LIC), iron filings, field vectors, and 3D field lines.

A closed-path integral tool supports investigations of Ampère's law on user-drawn loops. Charged-particle trajectories in 2D and 3D illustrate magnetic forces with adjustable initial conditions. Example investigations include Helmholtz-coil field uniformity, solenoid fields, magnetic dipoles, and cyclotron motion.

The simulator supports lecture demonstrations, pre-lab visualization, computer-based lab activities, and student inquiry in AP Physics C: Electricity and Magnetism, IB Physics, and introductory university E&M courses. Scenes can be shared by URL and embedded via iframe in course pages. It runs in modern desktop and Chromebook browsers, with no installation or registration required.