No. Everything runs in this browser tab on your own device. Engines are downloaded once and cached, but your files never leave your computer.

Are my files uploaded?

No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.

Is it free? Are there limits or watermarks?

Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.

Does it work offline?

Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.

Home / 3D / STL Inspector & Repair

STL Inspector & Repair

Check STL files before printing: size, volume, weight estimate, watertight and manifold checks, normal flipping and triangle reduction.

Free, no uploads, no sign-up. Runs 100% in your browser.

How STL Inspector & Repair works

The mesh is welded and analysed on your device: signed volume, surface area, bounding box, open (boundary) edges, non-manifold edges, zero-area triangles and separate shells. Fixes include flipping inverted normals, removing bad triangles, centring on the plate, unit conversion and simplification with meshoptimizer.

Input: STL, OBJ, PLY, 3MF, OFF, AMF, GLB. Output: STL.

How to use STL Inspector & Repair

Drop an STL (or OBJ, PLY, 3MF).
Pick the file units and your filament.
Read the report and apply fixes if needed.
Download the fixed STL.

Tips

A model with open edges may still slice, but closing holes in your CAD program gives cleaner prints.
Weight is an estimate. Your slicer gives the exact number.

STL Inspector & Repair FAQ

Is my file uploaded?: No. Everything runs in this browser tab on your own device. Engines are downloaded once and cached, but your files never leave your computer.
Are my files uploaded?: No. This tool runs entirely in your browser tab. Files are read from your disk into memory and the result is generated locally.
Is it free? Are there limits or watermarks?: Free and open source (MIT). There are no file-size caps, daily quotas, accounts or watermarks.
Does it work offline?: Yes, once the page (and any engine it needs) has loaded, it keeps working without a connection thanks to the service worker cache.

Related tools

3D Model Viewer: View GLB, GLTF, OBJ, STL, PLY, FBX, 3MF, DAE, 3DS, USDZ, AMF, VRML, OFF and point clouds with orbit controls, lighting, wireframe and screenshots.
Image to Lithophane (STL): Turn a photo into a 3D-printable lithophane or relief heightmap STL, flat or curved, with a live 3D preview.
3D Model Converter: Convert 3D models between GLB, glTF, OBJ, STL, PLY and USDZ, with unit scaling, centring and Z-up fixes.
GLB / glTF Optimizer: Shrink GLB and glTF files with Meshopt compression, quantisation, mesh simplification, deduplication and WebP texture resizing.