Free STL Viewer: no install, no account, nothing uploaded

The file is parsed the moment it lands on the page. A binary STL is read straight from its 50-byte triangle records; an ASCII STL is scanned line by line. The mesh is uploaded to your graphics card, not to a server, and drawn with a simple studio light so shape reads clearly. The camera frames the model automatically, so a 5 mm nozzle test and a 300 mm helmet both fill the view.

• Orbit with the left mouse button or one finger, pan with the right button or two fingers, zoom with the wheel or a pinch. Double-click to re-centre.
• Wireframe shows the triangles, which is how you judge mesh density and spot slivers.
• Colour picks the surface colour; useful when the default grey hides detail on a screenshot.
• Section switches on a clipping plane you can slide through the model to look inside a hollow part or check a wall thickness by eye.
• Measure takes two clicks on the surface and reports the straight-line distance in mm or inches.
• Dimensions shows the bounding box, volume, surface area, counts and the watertight check; the mm / in toggle switches units.
• Screenshot saves the current view as a PNG.

Like every tool on this site, the work happens in your browser. The file is read from your device, parsed in memory and drawn with WebGL; no copy is sent anywhere. Open the network panel of your browser's developer tools while you load a model and you will see no upload. Close the tab and the model is gone.

A 150,000,084-byte binary STL is exactly 3,000,000 triangles: subtract the 84-byte header and count, divide by 50. That is a dense scan of a car seat, say seat.stl, and the kind of file that makes an online viewer with an upload step give up.

1. Drop the file. Parsing three million triangles takes a few seconds on a laptop, and the page shows progress rather than a blank screen. Nothing is transferred, so there is no upload bar.
2. The status line reads 3,000,000 triangles, 1,500,412 vertices, 1,120 x 640 x 980 mm. A car seat is about that size, so the scanner exported in millimetres.
3. Orbit. Three million triangles is fine for a discrete graphics card and a little sluggish on an integrated one; the viewer draws the model as one mesh so there is no per-object overhead.
4. Switch on Section and slide the plane through the seat back. The mesh is a single surface, not a solid, and the section shows a thin line rather than a filled area. That tells you the scan has no thickness and would need to be shelled before printing.
5. Check the watertight line: no, 8,412 open edges. Expected for a raw scan; see STL repair for the counts and a mesh editor for the closing.
6. Take a Screenshot of the section view and send it.

On a phone the same file may not fit in memory. Decimate it on a desktop to a few hundred thousand triangles first; for a visual check that is more than enough.

• W toggles wireframe, S the section plane, M measure mode, F re-frames the model, D dark mode.
• The viewer reads binary and ASCII STL, OBJ, GLB and glTF, 3MF and PLY. Format is detected from the content, so a mislabelled file still opens.
• Drop several files and only the first opens; the notice tells you so. Open the others one at a time.
• The page installs as an app (Chrome, Edge, Android, iOS Add to Home Screen) and then works offline.
• Your colour and unit choice survive a reload; the model does not, because it was never stored.

• No STEP, IGES or other CAD formats yet. Export a mesh (STL, OBJ, 3MF) from your CAD tool first.
• No G-code preview. Use your slicer for toolpaths.
• Textures referenced as separate files (OBJ + .mtl + images, .gltf + .bin) are not loaded; embedded textures in GLB are.
• The whole file is held in memory. A few hundred MB is fine on a laptop; phones have far less headroom.
• No editing beyond repair and conversion. There is no sculpting, boolean or hole filling.