Broken triangles
Removes flattened or incomplete triangles that can cause slicer errors.
Fix common STL problems before printing
Free Online STL Repair Tool
Upload, check and repair broken STL files before 3D printing. Find common problems, preview the model and download a repaired STL.
No software installation No file upload Preview before download Free basic STL repair
File stays private
Ready to download
X
Y
Z
Free STL check and repair
No upload requiredCheck and repair your STL
Drop an STL file to get started
Drag and drop or choose a file
ASCII or binary STL · Maximum 50 MBLoading 3D preview…
Your model stays on your device. STLFixer does not upload your file.
Clear repair results
What STLFixer Can Fix
STLFixer repairs common file problems and clearly shows any issues that still need attention.
Duplicate faces
Removes faces that appear more than once in the same place.
Face directions
Refreshes face directions so slicers can read the model correctly.
Open edges
Finds holes and non-manifold edges that may need advanced repair.
Four clear steps
How to Repair STL Files Online
- 01
Upload
Choose an STL file up to 50 MB. Your file stays on your device.
- 02
Check
Review the model size, triangle count, holes and problem edges.
- 03
Repair
Fix common problems and compare the file before and after.
- 04
Download
Download the repaired STL and open it in your slicer.
Print with fewer surprises
Why STL Files Need Repair Before 3D Printing
Broken faces, duplicate surfaces and open edges can cause missing layers, unwanted walls or slicer warnings.
Checking the STL before slicing lets you fix common problems early. If holes or non-manifold edges remain, the results will tell you that advanced repair may still be needed.
Learn about watertight STL filesKnow the limits
Basic STL Repair vs. Advanced Mesh Editing
Use basic repair for conservative cleanup. Move to a mesh editor or the source CAD model when the intended shape must be rebuilt.
Removable face problems
STLFixer can remove collapsed triangles and repeated faces, then export refreshed face directions without scaling the model.
Open and non-manifold edges
The tool counts edges that indicate holes or invalid joins. These results stay visible when the correct replacement surface needs manual judgment.
Holes and intersecting shells
Use Blender, CAD software or another advanced repair tool to create missing surfaces, join solids or remove internal geometry.
Slicer layer preview
Check dimensions, thin walls and every generated layer before printing. A repaired topology report is not a guarantee that a model is printable.
After repair
What to Do Next
Edit the model, prepare it for printing or create a new 3D model from scratch.
Generate a new 3D model
Start from text or an image
Edit your model
Make detailed changes to its shape
Prepare for 3D printing
Slice and configure the print
Some links may be affiliate links. We may earn a commission at no extra cost to you.
Straight answers
Frequently asked questions
Is STLFixer really free to use?
Yes. You can check, preview, repair and download an STL file for free.
Are my STL files uploaded to a server?
No. Your STL file stays on your device and is not uploaded to STLFixer.
Which STL formats are supported?
You can open both binary STL and ASCII STL files up to 50 MB. Repaired files are exported as compact binary STL files.
What problems can the STL repair tool fix?
Basic repair removes broken triangles and duplicate faces, then refreshes face directions. It can detect holes and non-manifold edges, but it does not fill or rebuild them yet.
Can STLFixer make every file watertight?
No. STLFixer finds open and non-manifold edges, but it does not fill holes yet. A mesh editor may be needed when open edges remain.
Why does STLFixer not show millimeters or inches?
STL files do not record whether a model uses millimeters, inches or another unit. Use the same unit you selected in your modeling or slicing software.