OpenCascade.jsWhat is OpenCascade.js
One-page concept — what OpenCascade.js is, why it exists, and when to reach for it.
@taucad/opencascade.js brings the OpenCASCADE Technology kernel — a 30-year-old
production-grade BRep CAD library — into the WebAssembly runtime. Every public
OCCT symbol the package configures becomes a TypeScript class with overloaded
constructors, typed methods, and full .d.ts coverage.
Why a CAD kernel in WebAssembly
Browser-native CAD historically meant polygon-only mesh editing. A BRep kernel gives you:
- Exact geometry — curves and surfaces are analytic, not polygonal. Booleans, fillets, chamfers, threads all run on parametric primitives.
- Standards-grade interchange — read and write STEP (
AP214/AP242), IGES, STL, and GLB out of the box; no external tooling required. - Full feature parity with desktop CAD —
BRepPrimAPI_*primitives,BRepAlgoAPI_*booleans,BRepFilletAPI_*fillets,XCAF*for assemblies and materials.
When to use OpenCascade.js
| Use case | Good fit | Bad fit |
|---|---|---|
| Parametric CAD app | Yes | — |
| STEP / IGES interchange | Yes | — |
| Procedural mesh generation | Yes | three.js or manifold-3d may be lighter |
| Real-time interactive booleans (>60 fps) | Maybe — measure first | Reach for manifold-3d |
| Cloud STEP-to-GLB conversion | Yes | — |
When NOT to use it
- You only need polygon meshes —
three.js+manifold-3dis smaller and faster. - You need sub-megabyte wasm — full OCCT is ~38 MB; even trimmed it sits at ~12 MB for a typical "box + boolean + export" surface.
- You need synchronous-only call sites — every
initreturns a Promise.
Where to next
- Quickstart — npm — render a box in 20 lines of TypeScript.
- Trim symbols — cut the wasm from 38 MB down to what your app uses.
- API Reference — search every bound class and method.