Open an STL file to see a shaded 3D preview you can rotate and zoom, along with its triangle count and overall dimensions.
The file is opened locally in your browser and is never uploaded.
This viewer reads both binary and ASCII STL files, builds the triangle mesh in your browser, and renders it with flat shading so facets are easy to inspect. Drag to rotate, scroll or pinch to zoom, use the wireframe overlay to see the underlying triangulation, and use Reset view to return to the starting angle. The dimensions are the size of the axis-aligned bounding box around the model, in the units stored in the file, which most slicers interpret as millimetres. Nothing is uploaded: the file is read with the browser FileReader API and drawn with WebGL on your device.
Does this viewer upload my STL file? No. The file is opened locally with FileReader and rendered on your device. Nothing is sent to a server.
Why does my model look faceted? STL files store flat triangles with no smooth shading information beyond facet normals, so curved surfaces show their triangles. The wireframe overlay makes that triangulation visible.
What if the model opens very small or very large? The viewer fits the camera to the bounding box automatically. STL has no unit field, so a model modelled in inches will appear 25.4 times smaller numerically than the same model in millimetres.