FixSTL

FixSTL is a free STL checker and repair tool that runs entirely in your browser. Drop an ASCII or binary STL (up to 100 MB, about 2 million triangles), or up to 20 files at once, and it counts the problems that commonly break slicing: holes and open boundaries, non-manifold edges and vertices, flipped normals, self-intersections, duplicate and degenerate faces, and separate shells.

Repair is conservative by design. It welds nearly coincident vertices, removes duplicate and zero-area triangles, makes face orientation consistent and closes small, nearly flat holes. Every repair is compared with the original surface and discarded if it would move the shape beyond tight limits. The repaired file is re-checked before it is called fixed, and the report tells you plainly what remains — self-intersections are reported, not rebuilt, and wall thickness is not evaluated.

Your model is read and processed on your device in a Web Worker; it is never uploaded. No account, watermark or download limit. Because it is a web page, it works on Mac, Windows and Linux. FixSTL is built by Tripo.