Exact CAD geometry,
written in TypeScript.

A real B-Rep kernel in your browser via WASM. A type system that makes invalid geometry uncompilable. And a verification loop so AI agents author parts that are provably correct — not just plausible.

Open the Playground Get Started Authoring with AI →

v18 · Apache-2.0
OpenCascade kernel
STEP-accurate
runs in the browser

B-Rep vs mesh

Exact boundaries, not triangle soup.

Shapes are real mathematical boundaries — faces, edges, and vertices — so booleans are precise, measurements are real numbers, and STEP exports drop cleanly into SolidWorks, Fusion, and FreeCAD. No tessellation error baked into your model.

A turned part as an exact B-Rep solid — smooth curved face, clean edges — **brepjs** — exact B-Rep, one smooth face

The same part as a coarse triangle mesh — a faceted polygon approximation — mesh CAD — faceted triangle approximation

Type safety

If it compiles, the geometry is valid.

Branded types, Result<T, E>, and phantom types encode topological invariants in the type system. A ClosedWire, an OrientedFace, a ValidSolid mean exactly what they say. Malformed geometry doesn't fail at runtime — it fails to compile.

face.ts — tsc --strict

const w = unwrap(wire([line(a, b), line(b, c), line(c, a)]));

const f = filledFace(w);
                     ~
// TS2345: Argument of type 'Wire' is not assignable
//   to parameter of type 'ClosedWire'. Property
//   '[__closed]' is missing in type 'Wire'.

// prove it closed first — now it compiles
const ok = filledFace(unwrap(closedWire(w))); // ✓

The verify loop

CAD an agent can prove.

The hard part of AI plus CAD isn't drawing a shape — it's knowing it's correct. brepjs answers twice: the type system rejects invalid geometry before it runs, and brepjs-cad runs the part on a real kernel and returns a deterministic report — validity, measured dimensions, multi-view snapshots, a STEP export. Ships as a Claude Code skill and a CLI.

agent · verify loop

$ /plugin install brepjs@brepjs   # the skill
$ npm i -D brepjs-cad             # the runtime

> /brepjs:cad a 1×1 gridfinity bin
› brainstorm → design → implement → verify
✓ valid Solid · vol 14 043.4 mm³ · 91 faces
✓ assertions 3/3 · wrote bin.step

report.json · deterministic

ok: true shape verified

shapeType: "Solid"
checks.isValidSolid: passed ✓
measurements.volume: 14043.4
measurements.area: 11659.6
measurements.bounds: 41.7 × 41.7 × 30.5
topology: 91 f · 192 e · 104 v
topology.manifold: true
assertions.volume: 14043.4 = 14043.4 ✓

Point your agent at a spec; get back a part you can manufacture.

Engine-agnostic

Two kernels. One API. One line to switch.

occt-wasm — OpenCascade compiled to WebAssembly, about 4.7 MB brotli, Web Worker–ready — ships today as the default. brepkit, a Rust kernel built for speed (≈1 MB brotli), is a drop-in replacement under active development. Your code doesn't change.

ships today

occt-wasm

OpenCascade · WebAssembly · ~4.7 MB brotli · Web Worker–ready

withKernel(id, …)

in development

brepkit

Rust kernel · built for speed · ≈1 MB brotli · drop-in

Ecosystem

Native to the stack you already use.

ESM, top-level await init, a Three.js mesh adapter, structured errors, web-worker friendly. Drops into Vite, Next.js, and React Three Fiber. brepjs produces the geometry; you render it however you like.

ESM
top-level await
Web Workers
Vite
Next.js
R3F

scene.ts

import { box, mesh, toBufferGeometryData } from 'brepjs/quick';
import * as THREE from 'three';
 
const data = toBufferGeometryData(mesh(box(30, 20, 10)));
 
const geo = new THREE.BufferGeometry();
geo.setAttribute('position', new THREE.BufferAttribute(data.position, 3));
geo.setAttribute('normal', new THREE.BufferAttribute(data.normal, 3));
geo.setIndex(new THREE.BufferAttribute(data.index, 1));

File formats

Round-trips with the tools you already own.

Import and export STEP, STL, IGES, glTF, DXF, 3MF, and OBJ, plus 2D DXF/SVG profiles and OCCT BREP. Move exact solids between brepjs, SolidWorks, Fusion, and FreeCAD over STEP without losing precision.

STEPin · out
IGESin · out
STLin · out
OBJin · out
3MFin · out
glTF / GLBin · out
DXFin · out
BREPin · out
SVGin · 2D

Scope & fit

Built for exact, manufacturable geometry.

Boundary representation is the language of mechanical CAD — exact solids to micron precision, and the native form of STEP, CNC, and inspection. That's brepjs's strength: precise booleans, fillets, chamfers, and shells; real volumes, areas, and clearances; watertight solids that move cleanly between SolidWorks, Fusion, and FreeCAD. From a single bracket to a full assembly — enclosures, fixtures, gridfinity bins, machined and molded parts. It's a programmatic library, not a GUI, and exact B-Rep isn't the tool for organic sculpting or dense lattices; knowing that is part of why it's dependable.

Born from a tool people actually use — brepjs grew out of the Gridfinity Layout Tool.

v18
Apache-2.0
OpenCascade kernel
STEP-accurate
runs in the browser

Write your first solid.

Open the Playground Read the docs

Authoring with AI? Set up the brepjs-cad skill →

Exact CAD geometry,written in TypeScript.