About
STL File Viewer is a browser-based inspector for six 3D formats: STL, OBJ, GLB, glTF, FBX and 3MF. It covers the moment before a model is sliced, imported or sent to someone else — open the file, look at it, and read what it actually contains.
What the viewer does
A file opens into a viewport framed to fit, with orbit, zoom and pan, plus fixed front, top and right views for the questions a trackpad answers badly. Four panels describe what was read: the format and version, triangle and vertex counts, the bounding box in the model’s own units, every material with its texture maps, every animation clip with its duration, and a list of references that did not resolve.
The current view saves as a PNG at 1× or 2×, on the page background or transparent. It is the picture that goes into a bug report, a message to a client, or a note next to a print that failed.
What it is not
Not a repair tool, a converter or a slicer. It does not close holes, flip inverted faces, decimate a mesh, or write a different format. A model that is broken in the file looks broken here — and the Issues panel names what was found rather than hiding it, which is more useful than a clean preview that fails at the printer.
Why nothing is uploaded
The site is a set of static files. There is no endpoint to post a model to and no code that opens one: the file is read through the browser’s own file picker or a drop on the page, and it stays in that tab. This is a property of the architecture rather than a promise in a policy — changing it would take a new backend, not a settings toggle.
What the numbers mean
Dimensions are reported in the unit the file declares, and STL declares none, so a 20-unit part could be 20 mm or 20 inches. Each format page states what that container does and does not carry. Triangle counts are what the file holds, not what a slicer produces after repair.
Where a value is absent it shows a dash. A mesh with no material does not report zero materials; the file declared none, and zero would be a different claim.
Who maintains it
One developer builds and maintains the site. Parsing comes from the loaders in three.js at the version pinned in the build; the viewport and the panels are the site’s own. Where a format is only partly supported — FBX builds below the minimum the loader accepts, KTX2 textures, multi-colour 3MF — the format page says so instead of rounding it up.
How files are handled is on the privacy page: what stays in the tab, what the network can see, and the model data that is never collected. The terms cover what a successful load does and does not tell you.