How JustFixSTL Works
Your mesh files are processed entirely in your browser. Here is exactly what happens under the hood.
Browser-Side Processing
JustFixSTL runs entirely in your web browser. When you load a mesh file, every step — analysis, repair, and export — happens on your device. No file is ever sent to any server, and no external service processes your data.
Technical Implementation
The tool is built on these technologies and open-source libraries:
WebAssembly (WASM)
The technology that lets compiled C++ code run at near-native speed inside your browser. It is the foundation that makes browser-based mesh repair practical — no plugins or server round-trips required.
PMP — Polygon Mesh Processing Library
An open-source C++ library for geometry processing. It provides the core algorithms for detecting and repairing non-manifold edges and vertices, filling holes, fixing normals, and removing degenerate triangles.
meshfix-wasm
A custom Emscripten build of the PMP library compiled to WebAssembly. This is the repair engine that runs inside your browser. It is not yet published publicly; open-sourcing the WASM build is planned once stability is confirmed across a broader range of real-world meshes.
View on GitHub →File API & Blob URLs
Files you select are read directly into browser memory via the File API. Repaired meshes are created as Blob objects and offered as downloads. No network request is made at any point in this process.
Three.js (WebGL)
The 3D viewport uses Three.js to render your mesh in real time and highlight detected issues such as non-manifold edges and holes. All rendering happens locally on your device's GPU via WebGL.
What This Means for Your Privacy
- Your files are never uploaded to any server
- No third party receives or processes your mesh data
- We have no access to the content of your files
- No file data is logged or stored anywhere
- Files exist only in your browser's memory during processing
How to Verify
You do not have to take our word for it. Here is how to confirm:
- 1 Open your browser's developer tools (press F12, or right-click and choose Inspect)
- 2 Go to the Network tab
- 3 Use the tool to load and repair a mesh file
- 4 Observe: no outbound requests contain your file data
Alternatively, disconnect from the internet after the page loads. The repair tool continues to work — because it requires no server.
Trade-offs and Limitations
Because processing happens on your device, performance depends on your hardware. Very large mesh files may take longer to repair on slower or low-memory devices than server-based tools. The tool processes one file at a time. These are the trade-offs for keeping your files completely private.