STL repair
Slicer refusing your STL, or the print coming out hollow? Drop it here and the repair tool welds the cracks, fills the holes and fixes the normals — all in your browser, nothing uploaded — then hands you a watertight STL ready to slice.
Everything runs in your browser — your STL is never uploaded. Repair welds split vertices, fills open holes and recomputes normals; a hole gets a simple cap, so for a pristine surface, remesh in Blender.
What it actually does
Most “not watertight” and “non-manifold” errors come from three fixable problems, and this tool runs all three in one pass:
- 1. Weld split vertices
- AI and scan meshes often store each triangle's corners separately, so a solid surface looks cracked to a slicer. Welding coincident vertices stitches those seams shut — frequently the single fix that clears the warning.
- 2. Fill open holes
- A missing face on the back or underside leaves an open boundary. The tool finds each hole and caps it, so the surface closes into a single watertight shell. Complex holes get a simple cap — good enough to slice, not a work of art.
- 3. Recompute normals
- Faces pointing the wrong way (the dark ones in a viewer) confuse the inside/outside test. Recomputing normals sets them consistently so the slicer reads the model correctly.
It's the in-browser version of the repair paths in our guide to making an STL watertight — try this first, and fall back to Blender or Meshmixer only when it reports open edges it couldn't close. To see the problem before you fix it, open the file in the STL viewer and switch to wireframe.
How to repair an STL
- 1Click “Repair an STL,” or drag your .stl onto the box — it repairs locally, with no upload.
- 2Read the result: welded cracks, holes filled, and whether the mesh is now watertight.
- 3Download the repaired STL and slice it — or, if open edges remain, remesh it in Blender.
STL repair — FAQ
- What does this STL repair tool fix?
- Three of the most common reasons a slicer rejects an STL: split (unwelded) vertices that leave a solid mesh looking cracked, open holes where faces are missing, and flipped or inconsistent normals. It welds coincident vertices, caps each open hole, and recomputes normals, then reports whether the result is watertight.
- Is it really free and private?
- Yes. There's no sign-up and no upload — your STL is read and repaired entirely in your browser with WebGL and JavaScript, so a confidential or client model never leaves your device. Repair as many files as you like.
- Will it make my STL watertight for printing?
- For the common cases, yes — welding split vertices and capping open holes clears most “not watertight” and “non-manifold” warnings. It tells you directly whether the result is watertight after repair. A very broken mesh (many overlapping shells, self-intersections) may still have open edges, and the tool says so.
- It says open edges remain — what should I do?
- That means a hole was too complex for a simple cap, or the mesh has non-manifold structure a weld can't resolve. Those are the cases for a voxel remesh in Blender (or Meshmixer's Make Solid), which rebuilds the whole surface as one watertight body at the cost of some surface detail.
- Can it repair a file that isn't an STL?
- This tool works on STL. If your model is a GLB, OBJ or other format, convert it to STL first with the free converters, then repair it here.
- How is this different from my slicer's repair?
- It overlaps — a slicer's fix pass also welds and closes simple holes. The advantage here is that you see exactly what happened (open edges before and after, holes filled, watertight or not) and get a clean STL back to reuse anywhere, rather than a black-box fix buried in one print job.
More free 3D tools
Need a model to print?
Describe it or drop in a photo — Sculptor generates a 3D model and exports print-ready STL, which you can check and repair right here.
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