STL Checker
& Repair
See exactly what is wrong with your mesh before anything touches it: open edges, non-manifold geometry, flipped normals, duplicate faces, debris. Then repair it to a watertight STL and verify the dimensions still match. Every step is shown, nothing is fixed silently.
Free for files up to 25 MB, no signup. Files are deleted automatically within 24 hours.
Drag & drop files here or Browse
Auto-detects CAD, Video, PDF, and 200+ formats
What the Report Covers
The same diagnosis runs in both modes, streamed live to the job console and included in the downloadable report.
Watertightness
Open boundary edges mean the mesh has holes and encloses no volume — the top reason slicers refuse a file.
Non-manifold edges
An edge shared by more than two triangles. The slicer cannot tell inside from outside.
Face winding & normals
Flipped triangles make parts of the model read as inside-out.
Duplicate & degenerate faces
Doubled-up or zero-area triangles, typically left behind by boolean operations and bad exports.
Shells & debris
Disconnected fragments and floating noise triangles, common in scan output.
Dimensions & volume
Bounding size and enclosed volume, before and after repair — so you can verify nothing drifted.
How It Works
Inspect
The mesh is welded and measured: triangle and shell counts, open boundary edges, non-manifold edges, winding consistency, duplicates, dimensions, and enclosed volume. In check mode this is the whole job — you download the report and your file is untouched.
Repair
Cheap fixes first: dedup, normals, hole filling, debris removal. Only if defects remain does the surface get rebuilt (pymeshfix), rejoining cracked fragments. The console shows each step as it happens.
Verify
The diagnosis runs again on the result. Before/after dimensions and volume are printed side by side, with a warning if anything moved more than 1% — so a repair never changes your part behind your back.
What repair can and cannot do
Closing holes, removing duplicates, and fixing normals does not move geometry. Welding hairline cracks can: in our worst validation case, a badly cracked mesh lost volume during reconstruction. The report prints before/after numbers precisely so you can catch this — if a dimension is critical, measure it after repair.
Open surfaces (a plane, a relief, a scan patch) are flagged as "surface, not a solid" rather than force-closed into something misleading. And a small number of files are damaged beyond automatic repair; when that happens the report says so and the output is delivered as-is improved, not advertised as fixed.
Repairing for CAD instead of printing? A repaired STL is still a mesh. To edit dimensions or send a file to a machinist, convert it to STEP with the STL to STEP converter after repairing it here.