STL Checker for 3D printing.
Upload an STL to find open edges, non-manifold geometry and degenerate faces before slicing — plus dimensions, volume and mesh counts. Runs locally in your browser; nothing is uploaded.
Choose an STL file
Check topology and print-readiness locally in your browser.
ASCII and binary STL supported.
What the checker looks at
Open edges (a triangle's edge with no neighbor — usually a hole), non-manifold edges (an edge shared by three or more triangles, which makes "inside" and "outside" ambiguous), and degenerate faces (zero-area triangles). Alongside that: triangle count, welded vertex count, bounding-box dimensions, and signed volume — all computed directly from the mesh, not estimated.
A zero-error result means the model passes these topology tests — it does not check wall thickness, overhangs, supports, or printer-specific tolerances. Always give the toolpath a final look in your slicer before printing.
FAQS
What does this STL Checker check?
It checks open edges, non-manifold edges and degenerate faces, then reports triangle count, unique vertices, bounding-box dimensions and signed volume. It also shows a local 3D preview.
How do I check if an STL is watertight?
Choose the STL file above. A closed manifold surface should have zero open edges and zero non-manifold edges. STL Check also flags zero-area faces because they can destabilize slicing.
What is a non-manifold edge in an STL?
It is an edge shared by three or more triangles. That makes the inside and outside of the surface ambiguous, so a slicer may interpret the model incorrectly.
Can STL Check repair a broken STL file?
It can attempt repair for the topology issues handled by the browser repair engine. Repair is secondary to checking, and the result is validated again before a file is named repaired.
Does a zero-error result guarantee a successful 3D print?
No. This checker validates the mesh topology tests shown in the report. It does not currently guarantee wall thickness, support requirements, overhangs, printer tolerances, material settings or a complete self-intersection analysis. Always preview the final toolpath in your slicer.
Does STL Check upload or store my STL file?
No. STL parsing, analysis, preview and repair run in this browser tab. The STL file itself is not uploaded by the checker.
Does it support both ASCII and binary STL files?
Yes. STL Check detects standard binary STL files first and falls back to ASCII STL parsing automatically.