STL Repair Online
See what is wrong with your STL, fix it in your browser, and check every change. No upload.
Binary or ASCII. It stays on this device.
We show what is wrong before changing anything, then what each fix did.
- Fixes open edges, flipped faces, duplicates, zero-area faces and inside-out parts, and keeps a hollow hollow
- Rebuild clears crossing faces and edges shared by 3 or more faces, and loses fine detail
- We test the file. We can’t promise how it prints
Before
Working…
After
Nothing changed yet
- Faces on a faulty edge
- New faces we added
Drag to turn both views.
This browser can’t show the 3D view (WebGL is off). The counts and the download still work.
What repair can and can’t do
Repair changes as little as it can. Faces that were fine stay where they were. Corners in a hairline gap move by a tiny amount to meet. A filled hole is a guess at a surface that wasn’t in your file, so we mark every new face and tell you the size of the largest hole.
Rebuild throws the surface away and makes a new one from what is inside the shape. It can fix files that repair can’t, such as edges shared by 3 or more faces and crossing faces. Detail smaller than its grid is lost, inner walls go, and the page shows the grid size, the volume change and the largest move we sampled before you download.
What the numbers don’t tell you
A closed file can still be too thin, need supports, or be the wrong shape. A part that’s missing from your file but sealed shut looks complete to any check, here or anywhere else. Open it in your slicer and look at the layers before printing.
STL has no units, so the sizes here are the numbers in the file, read as millimetres. The crossing-face count stops early on very dense files and says so, and such a file never reads as clean.
What was tested, and what wasn’t
We ran this page in a headless Chromium browser on 71 awkward files from our test set, 9 we made for this page and 6 real ones. Each repaired file was read by three separate programs: a verifier of our own, trimesh and numpy-stl. On our pawn with faults added, Repair put the volume back within 0.01% of the undamaged part. A sphere of 2.4 million faces took about 37 seconds to repair on our laptop. We haven’t tried Safari or Firefox, or a real phone, and we haven’t compared results with other repair tools.
Nothing here has been opened in a slicer or printed. MakerJig has no printer. Read how we test.
FAQ
How do I repair an STL file online?
Drop the STL here. The page lists its faults and marks them in red. Press Repair, look at what changed in teal, and download once the file reads back closed. No account and nothing to install.
Is my STL uploaded?
No. The file is read and repaired by this browser tab. Every test run logs the requests made while a file is in use, and none of them holds the file, its name or any part of it. The page still sends a page-view count and one “tool finished” count, which name the tool and not your file.
What does “not manifold” or “not watertight” mean?
Every edge of a solid should join exactly two faces. An open edge has one face, so there’s a hole. An edge with three or more faces is non-manifold. Slicers need to know what is inside the shape, and these faults make that unclear.
Repair or Rebuild: which do I use?
Start with Repair: it keeps your faces. Use Rebuild when Repair can’t close the file or faces cross. Rebuild replaces every face, so small detail is lost and inner walls go.
Will the repaired model look the same?
Repair keeps it the same apart from the teal faces it added. A big hole gets a simple patch, which can look wrong on a curved surface, so check it. Rebuild changes everything slightly, and the page shows how much.
Why is the download off?
The page writes the repaired STL and reads those bytes back. If an edge doesn’t join exactly two faces, or the file has no real volume, you don’t get it. A file that isn’t a solid at all, such as loose triangles, can’t be repaired into one.
Does a repaired file always print?
No. This checks the file, not the print. Thin walls, overhangs and missing parts can still spoil a print. We haven’t test-printed anything.
Can I also repair OBJ or 3MF?
Not here yet: this page opens STL. Convert first with OBJ to STL or 3MF to STL.
How large a file can it take?
400 MB on a computer and 100 MB on a phone. These are this page’s own limits, not measured phone limits. Rebuild uses the Standard grid on phones.
More free tools
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