STL Viewer: view STL files online, free

Yes. It runs in the browser with no signup, no watermark and no file size tier. There is nothing to install and nothing to pay for.

No. This is the part worth being precise about: the STL is read by your own browser and rendered on your machine. It is never sent to us, so there is no upload to wait for and nothing of yours sits on our servers. Our conversion tools do upload, because the work happens on a server. Viewing does not.

Bounding box dimensions in millimetres, centimetres or inches, triangle count, surface area and enclosed volume, plus a mesh check: it counts open boundary edges, which are holes, and non-manifold edges, where more than two faces share an edge. Both are drawn on the model, red for open edges and amber for non-manifold. Those are the two defects that make a slicer complain.

That is exactly what this is for. Most desktop STL viewers want an install and an account. Drop the file here instead and it renders immediately.

There is no server limit because nothing is uploaded, so the ceiling is your own machine. Meshes of a few hundred thousand triangles are comfortable. Above roughly 600,000 faces the edge analysis is skipped so the tab stays responsive, and the model still renders.

Yes, with the same touch controls: one finger to rotate, two to pan and pinch to zoom. Very large models are harder on a phone than a laptop, since the rendering happens on the device.

This viewer reads STL. For a STEP file, convert it to STL first and the result opens here. For other formats our converters will produce an STL you can then view.

Usually holes or non-manifold edges, which look invisible from outside because the surface still appears closed. The viewer marks both. If it finds them, the repair tool fixes that class of problem directly.

Yes. Open the options panel and pick from the presets or choose any colour you like for both. STL files carry no colour of their own, only geometry, so what you set here is purely how it is displayed. It is genuinely useful for looking at a shape: a light model on a dark background shows silhouettes and thin features that a mid-tone on mid-tone hides.

Yes. Cross-section in the options panel cuts the model with a plane: pick X, Y or Z and drag the slider to move the cut through the part. Flip shows the other half. It is the quickest way to check wall thickness, spot an unintended cavity, or see whether an internal feature actually came through the way you meant. The cut surface renders solid rather than as a hole, so the section reads properly.

Yes. Turn on point to point measurement and click two places on the mesh; the distance between them is shown in whichever unit you have selected. Dragging still rotates the model, so you can orbit to a better angle between clicks without dropping stray points. Clicking a third time starts a fresh measurement.

Yes. Save PNG snapshot in the options panel downloads the current view exactly as framed, including the colours you chose. Like everything else here it happens in the browser, so the image never touches a server.

Yes, in the options panel, and it changes the dimensions, surface area and volume together. STL stores no unit at all, so the file is assumed to be in millimetres, which is what slicers and CAD packages assume too. Switching to inches converts that assumption rather than reading anything from the file.

They are the bounding box of the geometry as stored in the file. STL carries no unit, so the numbers are assumed to be millimetres, which is what virtually every slicer and CAD package assumes too. A model authored in inches will read as millimetres here, as it would anywhere else.