CADgang

A CAD viewer and markup tool. Open a STEP, IGES, BREP, STL, OBJ, PLY, 3MF, glTF, GLB, FBX or DXF file, cut it, measure it, draw on it. The markups are anchored on the model and Claude Code can see them over MCP, so "the edge I circled" means something. Runs as a web page or as a Mac app that updates itself.

Earlier versions were a CAD authoring tool (a node graph of B-rep and distance-field blocks, then prompt-authored cells driving OpenCascade). That code is tagged v0.8.0-alpha.28-full; from 0.9 cadgang is the viewer.

Mac app

Download the latest cadgang-<version>.zip from the releases, unzip, drag to Applications. The app checks for updates on its own (Sparkle; cadgang → Check for Updates… does it now). Press Default in the toolbar once and Finder opens every supported file type in cadgang. Files open by double-click, by drop anywhere on the window, or with ⌘O. If a dev server is already on port 4477, the app adopts it.

To build it yourself: npm install && npm run build → dist/cadgang.app (Swift WKWebView shell, bundled node, Sparkle). npm run release builds, signs the zip for Sparkle, publishes the zip and appcast to the VPS, and creates the GitHub release.

Web

git clone https://github.com/cheewee2000/cadgang.git
cd cadgang && npm install
npm start          # → http://localhost:4477
npm test

No build step; the page is plain ES modules. CADGANG_PORT picks the port, CADGANG_DATA where markups and the last screen are kept. Local-path opens are allowed from the Mac app or from this machine, never through a proxy.

Tools

Bodies panel: one row per STEP body or DXF layer. Tick to hide, click a name to solo, shift-click for all. Explode slides bodies apart. Color gives each a hue.
Section: Off/X/Y/Z, drag the cut face or the slider, Invert the kept side. Cuts are capped, so hollow walls read as rings.
Measure snaps to endpoints, midpoints, centres and quadrants, defaults to axis-aligned distances (shift: free), reads a circle's ⌀ or an edge's length in one click, reads a cylinder's ⌀, a fillet's R or a sphere's SR from one click on the face, and measures face to face (parallel planes give the gap, anything else the closest approach). Dimensions stay on the page until clicked away or undone.
Markup: pen, arrow, note, erase. Anchored on the model, saved per file, and what cadgang_screen shows Claude.
Looks (shaded, metal, plastic, glass, x-ray, normals), ortho, edges, wire, grid, dark theme. These persist across sessions.
Undo/redo (⌘Z / ⇧⌘Z) covers every view change, dimension and stroke. Right-click opens the command menu; every button shows its hotkey on hover.
Rotation has no limits. Scroll rotates, shift-scroll pans, pinch zooms, double-click re-centres.
DXF drawings are paper: drag and scroll pan, two-finger spin turns in 90° steps ([ ] on a keyboard), Flip (B) turns the sheet over. Lines, polylines with bulges, circles, arcs, ellipses, splines and block inserts are drawn; text, dimensions and hatches are skipped and counted.
?open=/abs/a.step|/abs/b.stl, ?section=z:0.3, ?explode=0.4 set the viewer from a URL.

Key	Action	Key	Action
F	Fit	X Y Z	Section axis (again: off)
E W G O C	Edges, Wire, Grid, Ortho, Color	I / Esc	Invert section / cancel pick, section off
L	Next look	1–7	Front, back, top, bottom, right, left, iso
M	Measure	P A N R ⌫	Pen, Arrow, Note, Erase, Clear markup
B	Flip drawing over	[ ]	Turn 90°
D	Dark / light	⌘O ⌘Z ⇧⌘Z	Open, Undo, Redo

Claude Code (MCP)

The repo ships .mcp.json (and .codex/config.toml), so opening it in Claude Code registers the cadgang MCP server. Manually: claude mcp add cadgang -- node /path/to/cadgang/src/mcp/index.js. The app or npm start must be running; set CADGANG_URL if it is not on port 4477.

Tool	What it does
`cadgang_screen`	The live viewport as the user sees it, with their markups drawn on, plus the markups as 3D data (mm), the file on screen and the camera
`cadgang_markup_clear`	Remove the markups of the file on screen once acted on
`cadgang_open`	Open one or more files in the window

REST

Endpoint	Description
`POST /api/view/tessellate?name=…` (raw body) · `?path=/abs/…`	STEP/IGES/BREP → one binary buffer of triangles with B-rep face and body ranges
`GET /api/view/file?path=/abs/…`	Raw bytes of a local file (mesh formats parse in the browser)
`GET/PUT /api/view/markup?subject=…`	Markups of one file
`POST /api/view/snapshot` · `GET /api/view/screen?fresh=1` · `GET /api/view/screen.png`	The page posts what it shows; Claude reads it
`POST /api/view/open {paths}`	Tell open pages to open files
`GET /api/health`	Version and connected pages

ws://…/ws says hello with the server version (pages reload when it changed) and broadcasts markup_changed, snapshot_request and open.

Layout

src/server/index.js   Express + WebSocket; supervise.js restarts it if it dies
src/server/view.js    tessellate, local files, markups, screen, open
src/core/step.js      STEP/IGES/BREP → triangles with face and body ranges (occt-import-js, in a worker thread)
src/mcp/index.js      the three MCP tools
web/view.js           the page: loaders, bodies, section, undo, commands
web/measure.js        snaps, edge/arc classification, face fits, dimensions
web/dxf.js            DXF entities → line segments per layer
web/markup.js         pen, arrow, note on the model; the screen snapshot
web/orbitinput.js     trackpad: scroll rotates, pinch zooms, spin turns paper
mac/main.swift        WKWebView shell, file associations, Sparkle; build.sh, release.sh, the icon

Credits

three.js (MIT, vendored in web/vendor/) · occt-import-js (OpenCascade WASM) · Sparkle · Space Mono (SIL OFL 1.1, license in web/fonts/OFL.txt)

Built by CW&T with Claude Code.