Converts an STL or 3MF into a closed STEP solid, with optional smoothing that never risks the part's dimensions.
STEP (.step / .stp) is the standard 3D file format used by CAD software like Fusion 360, SolidWorks, Onshape, and Inventor. Unlike an STL, which is just a mesh of triangles, a STEP file describes exact solid geometry, so professional CAD tools can open, edit, and measure it precisely.
Most CAD programs can import STL files, but only as a mesh body that's hard to edit — you can't easily change dimensions, add features, or combine it with other parts. Converting to STEP turns the mesh into a solid body that behaves like native CAD geometry.
No. The entire conversion happens locally in your browser using WebAssembly — your file is never uploaded, stored, or sent anywhere. You can even disconnect from the internet after the page loads and the converter will still work.
Smoothing merges nearly-coplanar triangles into cleaner flat faces to reduce file complexity, but it never moves vertices beyond the tolerance you choose, so your part's outer dimensions stay accurate. You can disable it entirely if you need a 1:1 mesh-to-solid conversion.
You can upload .stl and .3mf files directly, or a .zip containing one of them, which is opened automatically. The output is always a standard .step file that opens in any CAD software.
There's no hard file size limit, but very dense meshes with millions of triangles can take one or two minutes to convert, since everything runs on your device's own processing power rather than a server.
Yes, it runs on any modern browser, including Safari on iPad and Chrome on Android, since it's a normal web page rather than a native app.
Yes, the converter is completely free with no sign-up. If you find it useful, there's an optional way to support the project below.