STLSTL
Repair STL files
Fix holes, flipped faces and loose triangles so your model slices cleanly. See exactly what was fixed.
- Nothing uploaded
- No sign-up
- Free, no limits
Drop your STL, OBJ or 3MF here
or paste it, or pick it from your device
.stl · .obj · .3mf
- Drop your STL file
- Check it in 3D
- Download the repaired file
Good to know
How to repair an STL file
- Drop your STL, OBJ or 3MF above. It's checked straight away and the problems are drawn in red.
- The repaired version is shown next to it. Switch between Original and Repaired to compare.
- Read what was fixed, change the options if you need to, and download the repaired file.
Your files stay on your device; nothing is uploaded.
What gets fixed
- Holes: gaps in the surface are found and closed with new triangles. Very large openings are left alone unless you raise the limit, because they're often on purpose (the top of a cup).
- Flipped faces: triangles that point inwards are turned to match their neighbours, and pieces that are completely inside out are turned the right way out.
- Cracks: corners that should touch but sit a hair apart are joined. Raise the tolerance for files exported with low precision.
- Junk triangles: zero-area and duplicate triangles are removed. Small floating bits (scan noise, stray faces) can be removed too.
What it can't fix
Two parts pushed into each other, surfaces that cross themselves and walls with no thickness (common in game assets and some AI-generated models) need a 3D editor such as Blender. Most slicers still print small leftovers fine: if the repaired file slices without warnings and the preview looks right, it's good to go.
Do I even need to repair?
Most slicers fix small errors when they load a file, often without saying so. Repairing first is worth it when your slicer warns about errors, the preview shows missing layers or odd gaps, or you want to split the model or convert it, which needs a closed solid.
Questions
How do I fix a non-manifold STL?
Drop it into the repair tool at the top of this page. Holes are filled, flipped faces are turned around and loose corners are joined, then you download the fixed STL or 3MF. Overlapping parts still need a 3D editor.
What does watertight mean for 3D printing?
The surface encloses a solid with no gaps: every edge is shared by exactly two triangles and every face points outwards. Slicers need that to tell inside from outside.
Why does my slicer say my model has errors?
The mesh has holes, flipped triangles or edges shared by more than two faces. It happens a lot with scans, game assets and models exported from CAD at low precision.
Will repairing change the shape of my model?
Only where it was broken. Holes get a flat or gently curved patch, and corners closer than the weld tolerance (0.001 mm by default) are joined. Everything else is left exactly as it was.
Is it safe to repair private or commercial models here?
Yes. The repair runs in your browser and the file never leaves your device.