ViSL3D generates interactive 3D visualizations of astrophysical spectral‑line datacubes by producing X3D and HTML output, viewable in a web browser via x3dom. It renders 3D structures of the datacube, overlays 2D images (e.g., optical or continuum backgrounds), and can display the positions of additional objects such as galaxies. Users can customize axis scales, colormaps, markers, and viewpoints, and interactively pan, zoom, rotate, and toggle visibility of components. Although developed primarily for radio datacubes, ViSL3D can be applied to other types of 3D astrophysical datasets.