Checker · watertight mesh
Watertight or non-manifold STL: know before the slicer complains
"Mesh not manifold", "non watertight", holes in the model: your slicer refuses the file or fills it unpredictably. Drop the STL: the tool counts open edges, finds edges shared by more than two faces and detects inverted normals, without uploading anything. It reports what it sees; it does not repair and guarantees nothing.
Nothing is uploaded: everything runs in your browser.
Watertight and manifold: two simple ideas
A mesh is watertight when every edge connects exactly two triangles: no opening, the inside is properly separated from the outside, and the volume can be computed. It is manifold when no edge belongs to three or more faces, which happens with nested shells or internal faces. Both defects confuse the slicer: it may fill a hole unpredictably or ignore an area.
What the tool measures, and what it does not see
It welds coincident vertices, then counts edges with a single face (open edges) and with more than two faces (non-manifold). It flags flat triangles and a negative volume, a sign of inverted normals. It does not detect self-intersections, thin walls or overhangs: those are checked in the slicer. A report with no defect is therefore not a print guarantee.
What to do with the defects found
A few open edges on a flat base: most slicers fill them. Dozens of open edges or non-manifold edges: repair in your modeling software (Blender, Meshmixer, your slicer's repair tool), then check again. The goal is zero open edges before slicing.
How it works
Drop the STL
Or a GLB / OBJ: the mesh is analyzed in your browser.
Read the counters
Open edges, non-manifold edges, flat triangles, normals.
Repair, then check again
In your 3D software or your slicer, down to zero open edges.
Frequently asked questions
- Zero open edges: will my STL print?
- Probably better, but it is not a guarantee. Self-intersections, wall thickness and supports are not checked here: verify them in the slicer.
- Why is the volume not shown?
- A volume only makes sense for a closed, manifold mesh. Otherwise the result would be wrong, so the tool does not show it.
- Does the tool repair the file?
- No. It measures and explains. Repair happens in modeling software or in the slicer, which offer automatic fixes.
- Is my file uploaded?
- No, everything is computed in your browser; nothing is uploaded.
Create a 3D model with AI
A photo or an idea becomes an STL and GLB 3D model. 150 free credits at sign-up, with a quote before every charge.