Fix broken or non-watertight STL files online free. Auto-detect non-manifold geometry, unclosed holes and inverted normals, repair in one click, and export STL or 3MF.
Open OwlCAD, drop your .stl onto the build plate, and run the built-in print check. It reports non-manifold edges and unclosed holes (the gaps a slicer can’t fill) and inside-out faces (inverted normals), and a one-click repair rebuilds the mesh into a watertight solid you can print.
Detect and resolve the geometry flaws behind failed prints, empty slicer layers, and sliced-open holes.
Find the holes, inside-out faces and paper-thin triangles your slicer can’t fill (unclosed mesh boundaries, inverted face normals and zero-thickness degenerate triangles), with the problem areas highlighted in the viewport.
Rebuild the mesh into a watertight manifold solid (closed, so a slicer reads it as solid), stitching open seams and closing holes, without redrawing your model.
Inspect overhang angles (the areas that would need supports) and minimum wall thickness against limits you set, resin drainage holes, and whether the model fits your FDM or SLA printer.
Drop your STL file onto the build plate, run the print check, repair defects, and export a clean STL or 3MF for Bambu Studio, PrusaSlicer, Cura or OrcaSlicer.
It opens on your device, it is saved to your workspace as you work, and it exports back out in the format your slicer wants.
Your browser reads and renders the model itself, so it appears as soon as you drop it in — you are never queued behind anyone else’s upload, and the file does not travel anywhere before you can see it.
Most online viewers forget your file the moment you close the tab. OwlCAD keeps the model in your own workspace and syncs it as you work, so it is still there when you come back to this browser. Create a free account and it follows you to any device, and your projects dashboard lets you delete anything you no longer want.
When you are done, export STL, 3MF, OBJ, GLB or STEP — the format your slicer or your colleague actually needs, not a project file that only opens here.
An STL file is non-watertight if its surface has missing triangles, self-intersecting faces, or unsealed boundaries, which leaves holes or inside-out faces a slicer can’t fill. Slicers need a solid, watertight manifold volume to compute print layers correctly.
Yes. The built-in print check measures bounding-box dimensions, volume, and triangle count, and flags overhang angles (areas that would need supports) and thin walls against the overhang angle and minimum wall you set, and checks that the model fits your selected printer’s build volume; a part too big for the bed can be cut into halves that key back together.
After repair, export your model as a clean, watertight STL, 3MF, OBJ, or GLB ready for any slicer, such as Bambu Studio, PrusaSlicer, Cura or OrcaSlicer — or as a STEP solid for mechanical CAD.