No upload · No account · Runs in your browser
Check an STL for holes, non-manifold edges, inconsistent winding, zero-area triangles, and disconnected shells in seconds. The mesh is analyzed on your own hardware and never uploaded, so a client's model can be checked without sending it anywhere.
Drop an STL file here
Binary or ASCII. The checker looks for topology defects that slicers repair silently — or not at all.
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Analyzing locally...
Could not read that file.
Open edges
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Non-manifold
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Degenerate
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Winding conflicts
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Shells
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File
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Format
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File size
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Triangles
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Unique vertices
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Bounding box
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Volume
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Surface area
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Edge checks at - merge tolerance. Volume is only exact for a closed mesh; a leading ~ means the mesh is open. Geometry only — wall thickness and overhangs are not tested.
Raise this for scans or files with slightly mismatched shared corners. Lower it for genuinely tiny features.
A boundary edge belongs to one triangle instead of two. That means a hole. A hole can make the slicer guess which side is solid, producing a missing wall or a hollow interior.
An edge shared by three or more faces. Often the ghost of a boolean operation: internal walls were left in place, or two solids overlap without being merged.
Adjacent triangles disagree about which side is outside. Slicers use winding to decide inside versus outside; conflicts can flip normals and confuse the volume calculation.
Degenerate triangles have no area and can trip slicers. Multiple disconnected shells are fine for a figure on a base, but a single object split into pieces may print apart.
What the result means, what it misses, and what to do next.
No. The STL is read from your disk, welded and analyzed in memory, and the result is rendered on this page. There is no upload request and no server-side analysis. Your file stays in the tab until you close it.
A watertight mesh has every edge shared by exactly two triangles, so its surface encloses a volume with no holes. Slicers need that closed volume to decide what is inside the model. If the mesh has open edges, the slicer has to guess or repair.
An edge used by more than two triangles. It usually comes from overlapping solids, zero-thickness fins, or a boolean operation that left internal faces behind. The slicer cannot tell which side is solid, so the result may be hollow, shifted, or missing.
No. Many slicers auto-repair small holes, and simple models often print anyway. The risk is that the repair is invisible and wrong: a hollow region, a missing wall, or a shifted shell. A watertight result simply removes that uncertainty before a long print.
The default is 0.001 mm, which merges vertices that are effectively identical. Raise it for scans or files exported with slightly mismatched shared corners. Lower it if the mesh has genuinely tiny features that must stay separate. The result always shows which tolerance was used.
No. This is a topology check: open edges, non-manifold edges, winding conflicts, zero-area triangles, and disconnected shells. Wall thickness, overhang angle, supports, resin suction, and print orientation depend on the model and the printer, and are not measured here.
No. It diagnoses the file and tells you what is wrong. Repair belongs in your modeling software or the slicer's repair tool. The converter changes format but deliberately does not pretend to fix geometry.
Help me build this properly
Does this actually solve your problem, or not?
I built this to answer one question: what percentage do I type into my slicer. But I don't know if that is where your workflow actually breaks. Tell me what is broken, missing, or just plain useless here. Honest answers, especially negative ones, are worth more to me than anything else you could do on this page.