STL Viewer
Open and inspect STL files directly in your browser. Rotate, zoom, view dimensions and check triangle count without uploading your model.
Your STL stays on this device. MeshWrench reads and renders it locally in your browser.
Binary or ASCII STL, up to 100 MB. This limit protects your browser from freezing — it isn't a Pro restriction.
Processed locally — nothing was uploaded.
- File size
- Encoding
- Triangles
- Width
- Height
- Depth
- Bounding min
- Bounding max
STL files don't store real-world scale. Selecting mm, cm or inches assumes the file's numbers are millimeters — the common convention for 3D-printing STLs — and converts the display only; it never changes the model itself.
How to view an STL file
- Select an STL file using the picker above (or drag one in once you're on the page).
- MeshWrench reads the file locally and parses it in a background worker — nothing leaves your device.
- Once parsing finishes, drag to rotate, scroll to zoom, and use the controls to fit the view or toggle wireframe.
What the viewer shows
After a file loads, the panel below the viewport shows file size, detected encoding (binary or ASCII), triangle count, width, height, depth and the bounding-box minimum and maximum. Every dimension is labelled in model units, since STL geometry doesn't carry real-world scale.
Binary vs ASCII STL
STL comes in two encodings. Binary STL packs an 80-byte header, a triangle count, and then a
fixed 50-byte record per triangle — compact and fast to parse. ASCII STL spells out each
facet as plain text (facet normal ... outer loop ... vertex ... endloop endfacet), which is far
larger but human-readable. This viewer detects which one a file uses automatically — including binary files
whose 80-byte header happens to start with the text "solid", which a naive detector would misread as ASCII.
Why STL dimensions are unitless
The STL format only stores triangle coordinates as plain numbers — it has no field for millimeters, inches or any other unit. A model might have been authored at any scale. That's why this viewer labels dimensions as "model units" rather than guessing a real-world unit, and why relabeling the display as mm/cm/in only changes the label shown, not the underlying numbers.
Is the STL file uploaded?
No. There is no server-side file-processing route in MeshWrench at all. Your browser reads the file with the standard File API, hands its bytes to a Web Worker running on your device, and renders the result with WebGL — also on your device. You can verify this yourself: open your browser's developer tools, watch the network tab, and load a file. No request containing your file will appear.
Common reasons an STL will not open
- The file is a truncated or corrupted binary STL — its declared triangle count doesn't match the actual file length.
- The file is ASCII STL with a malformed structure, such as a facet missing
endloop/endfacet, or with a vertex count other than three. - The file isn't actually an STL file, despite its extension.
- The file contains non-finite coordinate values.
- The model has more triangles than the free viewer's safety ceiling currently supports.
STL versus 3MF
STL stores only raw triangle geometry — no color, no units, no metadata, and often duplicated vertices between adjacent triangles. 3MF is a newer, XML-based format that can store color, materials, units and other metadata alongside the mesh. STL remains the most widely supported format across slicers and CAD tools, which is why it's MeshWrench's first viewer.
Frequently asked questions
Are STL files uploaded when I use this viewer?
No. Your file is read and parsed entirely in your browser, inside a background Web Worker. It is never sent to a server — you can confirm this yourself by checking your browser's network tab while a file loads.
Does this viewer support binary and ASCII STL?
Yes. It automatically detects which of the two STL encodings a file uses and parses it locally — you don't need to know or specify which one you have.
What units are the dimensions shown in?
STL files don't store real-world units, so dimensions are shown in model units by default. You can relabel the display as millimeters, centimeters or inches, but that only changes the label — it doesn't convert or modify the geometry.
Does this tool repair or validate my STL file?
No. This is a viewer only — it doesn't check for holes, non-manifold edges or flipped normals. STL Checker and STL Repair are planned as separate tools.
Is there a file size limit?
Yes, a safety ceiling protects your browser from freezing on extremely large models. It's a browser-stability limit, not a paid-tier restriction — every file under the limit gets the complete viewer for free.
Which browsers are supported?
Any recent version of Chrome, Firefox, Safari or Edge with WebGL and Web Worker support.