COSY turns a one-dimensional proton NMR spectrum into a two-dimensional correlation map: peaks sit on the diagonal exactly as in a 1D spectrum, but protons that are scalar-coupled through 2–3 bonds throw off symmetric off-diagonal cross-peaks. This simulator renders that 2D map as a live 3D contour surface — an InstancedMesh column for every (δ₁, δ₂) grid cell, height driven by the sum of Gaussian peak functions — for three real spin systems (1-propanol, ethyl acetate, ethylbenzene), each with a different J-coupling network. Adjust the acquisition linewidth and vertical scale, toggle the cross-peaks on and off to isolate the diagonal, and orbit the surface to see exactly which protons are talking to which.