STL & 3MF Viewer and Inspector

A watertight (closed, manifold) mesh has every edge shared by exactly two triangles, so it encloses a solid volume. Slicers need that to know what is inside the part. Open edges are holes; non-manifold edges are shared by three or more triangles; flipped-normal edges mean neighboring triangles disagree about which side is outside.

For a closed mesh, the viewer sums signed tetrahedron volumes from every triangle (the divergence theorem). It is the solid volume of the part, not the filament a slicer will use, which depends on infill, walls and supports.

STL files store bare numbers without units, and slicers read them as millimeters. A model exported in inches shows up 25.4 times too small, and one exported in meters 1000 times too small. Use the Units buttons to convert it before printing or converting to 3MF.

Yes. The viewer reads the core 3MF model, including objects stored in separate model files and build-item placements, in any 3MF unit. Colors, materials, plates and slicer settings are not shown.

No. Files are read and processed by JavaScript in your browser tab, and downloads are generated locally. Nothing is sent to a server, so it also works with private or unreleased designs.