brep-lens - STEP / B-rep inspector

Topology

problems only

Drop a STEP, IGES or BREP file here

or pick a sample above. Everything stays in your browser.

click: pick · drag: orbit · right/shift-drag: pan · wheel: zoom · F / double-click: fit · Z: zoom to selection · 1–6, 0: views · I / H / U: isolate, hide, show all · C: colours · O / L / N / S: orientation, flat, normals, section · V: vertices · Esc: clear · [ ]: back/forwardtap: pick · drag: orbit · two fingers: pinch-zoom and pan · double-tap: fit · long-press a tree row: isolate / hide

A STEP / IGES / BREP inspector that runs entirely in your browser: the file never leaves your machine. Geometry by Open CASCADE Technology compiled to WebAssembly, drawing by WebGPU.

Third-party software in this app

Component	Licence	Where
Open CASCADE Technology 7.9.3	LGPL-2.1 with the Open CASCADE exception 1.0	geometry worker (`breplens_core.wasm`), statically linked
Dawn / emdawnwebgpu v20260423.175430	BSD-3-Clause	renderer (`breplens_view.wasm`/`.js`)
Emscripten 6.0.13 runtime	MIT / University of Illinois NCSA	both wasm modules and their JS
musl libc	MIT	both wasm modules
LLVM libc++, libc++abi, compiler-rt	Apache-2.0 with LLVM exception	both wasm modules
dlmalloc	public domain (CC0)	both wasm modules
Vite module preload helper	MIT	app script

Open CASCADE Technology and relinking

This app uses Open CASCADE Technology, © 1999-2025 OPEN CASCADE SAS, under the GNU LGPL 2.1 with the Open CASCADE exception. It is linked statically into the geometry worker, and you are entitled to replace it with a modified version:

Exact source: tag V7_9_3 of github.com/Open-Cascade-SAS/OCCT (tar.gz), commit a016080b. No changes to OCCT's code; the build only leaves the XDE/OCAF packages out of two toolkits.
To relink: scripts/build-occt.sh wasm, then scripts/build-wasm.sh against your OCCT (see docs/BUILD.md). While the brep-lens repository is private, those scripts, our object files and the link line are available on request from the maintainer (GitHub: krispy-kenay).

Sample files

CTC-02 and CTC-05 are NIST Combined Test Cases, unmodified, from the NIST FTC/CTC PMI CAD models (National Institute of Standards and Technology, MBE PMI Validation and Conformance Testing project). Public domain (17 U.S.C. §105); thanks to NIST for making them available. Their use here doesn't imply NIST endorses this app. All other samples were generated for brep-lens with OCCT.

Full licence texts and notices (THIRD-PARTY-NOTICES.txt)