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.

https://github.com/user-attachments/assets/f583641c-d38d-479c-90d7-e1cd38e5bf87

The Mac app on the Wink camera enclosure: explode, section, markup, measure.

Try it: experiments.cwandt.com/cadgang — drop a file on the page or press ⌘O. The hosted copy cannot open paths on your disk; the Mac app and a local npm start can.

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; a file opened while another is on screen gets its own window (⌘N for an empty one). If a dev server is already on port 4477, the app adopts it. From a shell, /Applications/cadgang.app/Contents/MacOS/cadgang-open a.step b.dxf opens files in the running app without a second Dock icon.

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.

Related MCP server: Forge

Web

git clone https://github.com/cheewee2000/cadgang.git
cd cadgang && npm install
npm start          # → http://localhost:4477 (supervised; restarts if it dies)
npm run serve      # the bare server, for debugging
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 names to add them to the selection (SHOW ALL brings everything back), ✎ (or right-click a part → Rename…) to rename it. A rename is a label: it shows in the panel, the Joints panel and menus and is what Claude sees, but joints, marks and saved explode edits keep pointing at the part by its file name, so nothing breaks. It is saved with the file and in .cadgang projects. Explode slides bodies apart. A pin or bearing coaxial with a bore moves along the shared axis, parts mated on a plane separate perpendicular to it, a part between walls slides along the channel, a part in a pocket leaves by the open axis, anything loose goes out from the centre, and nothing travels through another body. The vectors solve on load up to 300k triangles; above that, press Solve next to the slider. Color gives each a hue.

• Select several parts and act on them together. Shift-click a part (or shift-click names in the Bodies list) to add it to the selection; shift-drag a window: left→right takes the parts fully inside it, right→left (dashed) every part it touches. A plain click selects one part, a click on nothing clears. The bar over the viewport then hides, shows, isolates (Only) or gives all of them one Material; H hides the selection, ⇧H shows everything, Esc clears. Panning is right-drag or shift-scroll (shift-drag pans only while a markup or measure tool is on).

• Bodies tree: rows sit in folders by assembly (STEP products, glTF nodes); a crowded folder gathers like-named bodies (every copy of one capacitor), repeated names get _1, _2, and a row reads name · material when the file names the material; ◐ makes a row or a folder transparent.

• Bodies rows are one line each: a name too long for the panel ends in … and its tip has it whole. Material, finish and colour sit in columns as wide as their longest word, the same place on every row, and are never cut; as the panel narrows the space between them shrinks first, then the names give way.

• Planes: Front, Top and Right reference planes through the model's centre, each on or off; + adds your own, offset from one of them by a distance or lying on a face you click. Front, Top, Right and offset planes follow the centre when parts move. Kept per file.

• Planes in the feature tree: a Planes folder at the top of the Bodies list holds Front, Top, Right and your own, each ticked to show. Right-click one to show or hide it; your own also rename, change their offset (Edit offset…), flip to the other side, or delete. Double-click your own plane's name to rename it.

• Weight, beside the size at the bottom: an estimate for the shown bodies, each body's volume times its material's density (Plastic 1.2, Aluminum 2.7, Steel 7.85 g/cm³…), in grams up to 1 lb, then pounds (567 g reads 1.25 lbs); with a selection it reads the selection's share first. Hover it for the split by material.

• Share (the share icon in the header): Copy screenshot puts a picture of the view, markups and notes included, on the clipboard to paste anywhere; Save screenshot saves it as a PNG named after the file; Share to web deploys a frozen copy of the view to your Vercel account.

• Ruler (⇧G) beside Grid: the grid's scale along its front and left edges, counting + and − from 0 at the grid crossing on the model's lower left corner seen from the top (the grid sits centred on the model with a line through that corner), in mm or in. In inches the grid steps every ½" with a darker line every inch, and the ruler numbers every inch.

• Move a part while exploded: press on it and drag it anywhere in the screen's plane (up and down too; ⇧ snaps to grid steps; a part in the selection moves the whole selection). That becomes where it explodes to: slide to 0 and it goes home, explode again and it comes back out to that spot (Reset clears it). Parts on it ride along, as do its markups; saved per file, undone with ⌘Z. Assembled, a drag rotates.

• Move triad (Triad on the selection bar, or Q), as in SolidWorks: on the selected parts, arrows (x red, y green, z blue) slide them along that axis and rings turn them about it; ⇧ snaps to grid steps or 15°. It stays one size on screen and is drawn over the model. Each part keeps the move as its placement (under any explode or joint), saved per file and undone with ⌘Z; Reset move puts the selected parts back where the file had them.

• Pictures: double-click one to edit it: drag to move, drag a corner to size, drag just outside a corner to rotate (⇧ in 15° steps), ⌘-drag a corner or an edge to crop; ⌫ deletes, Esc is done.

• 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 (as in Figma: click for corners, drag for curves, click the first point to close, Enter to end, ⌫ takes a point back), pencil (freehand), arrow, note, text (lies on the face clicked), image (a PNG or JPEG projected onto the surface; drag to size it), erase. Marks start only on the model: a press off it orbits the view, with any tool. Anchored on the model, saved per file, and what cadgang_screen shows Claude. Marks Claude has acted on turn Infinite Machine green at 30% and stay as a record.

• Several files: each browser tab or Mac window is one file with its own markups. New opens another; Claude's cadgang_open and cadgang_screen go to the tab or window you last touched.

• Modes (Explode / Joint in the toolbar, J switches): what a drag and the right-click menu do to a part. Explode: exploded, a drag places a part and ⌥-drag slides it along its axis (assembled, a drag turns the view), the menu sets its explode axis. Joint: drag moves a jointed part on its joint (anything else orbits), the menu adds joints, and explode is off so the assembly sits together. Joints keep their pose in both.

• The Joints panel folds: its − folds the whole panel to its head (Joints (n)), and each joint's own − folds it to its title line (type, part, ×), as the Bodies folders do. What is folded is kept in this browser. How to make and move joints is in the Joints title's tip (hover it), not always on the panel.

• Joints, as in Fusion: New joint (N, in Joint mode; or right-click → New joint…), click a face on the part that moves, then a face on the part it moves on (empty space: the ground), then pick the motion: Revolute / Slider / Screw / Cylindrical / Planar / Ball / Rigid. The first part snaps onto the second: flat faces meet face to face, round faces share an axis, centre on centre (Flip in its Joints row turns it over). The joint turns or slides about a round face of the two (a screw's shank, a bore, a pin), else the second face's normal, and the menu puts the type those faces suggest first. Planar slides the part about on the face and turns it on the normal: drag it, or set x, y and the angle in its Joints row. A part can have several joints: make another with New joint and it rides on the ones before it (a pin in a slot: Slider along the slot, then Revolute about the pin); a drag drives the one you last moved. Joints show what they join (dashed lines and an axis arrow) for a moment after one is made and while you point at the Joints panel. A sliding or turning joint also shows its range as a dashed track: drag the dot at either end to set min or max, double-click it to free it; in Joint mode the joint you last moved keeps its track up. Every joint but Ball has an offset along its axis (a gap under a part, a pin pushed further in): ⌘-drag the part to set it, or type it in the row. Then drag the part and it turns or slides on the joint (a screw turns and advances by its pitch; ⌥-drag a cylindrical joint to slide it), or use its slider in the Joints panel. Set what a joint is carried by (on), a screw's pitch, and min/max limits there. A screw's pitch starts as the ISO metric coarse pitch for its diameter. A joint's parent carries it: a screw in a lid follows the lid. Joints are saved per file, in .cadgang projects, and Claude can read and drive them (cadgang_joints, cadgang_joint). Annotate, then ask: write notes or arrows (double-click a tag to edit its text; Shift+Enter starts a new line) on the parts ("screw M3", "hinge", "lid slides on the pin"), then ask Claude Code to make the joints from your notes: it reads them with the round face each points at, makes the joints, drives each through its range to check it, and tells you what it made.

• Explode from the joints: SOLVE (and opening a file) reads how the parts are assembled. A screw, slider or cylindrical joint explodes along its own axis, out of the end with more room; a ball joint leaves by the open side of its socket; a part with a fixed joint has no travel of its own and goes with its parent; any part with a parent rides it. Parts are also staged: what stands in a part's way at rest comes off first, so the slider takes the outer parts away and then the ones under them. Parts with a clear way out are all in the first stage. Add or change joints and the explode solves again by itself (files over 300k triangles wait for SOLVE).

• Save / Open projects (⌘S, ⇧⌘S): a .cadgang file holds the model, markups, dimensions, joints, section, explode, camera and look. Open it with Open, a drop, or a double-click.

• 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.

• Select a body by clicking it in the view or the list, a whole part by clicking its folder (shift adds). H hides, T (or Transparent on the selection bar) makes it transparent, S shows only the selection, ⇧H shows everything, Esc deselects. Clicks pass through transparent bodies, so ghost the case and pick what is inside. The selection's menu sets its material (the MATERIALS look) and its colour (every solid look; a swatch, here or in a Bodies row, opens the colours the model already uses, then Other… for any colour), kept per file in the browser and undone with ⌘Z.

• STEP colours and material names the WASM importer misses (a style on a solid inside a part's compound, as Fusion writes them) are read from the file's text; the material name ("Steel - Satin") decides the MATERIALS guess first. An STL takes its body name from the file: an ASCII solid <name>, or the cadgang: <name> header cadgang writes.

• Named STEP export: a STEP that cadgang's cells write names every solid after the cell that made it (tray, lid), and a compound() of cells keeps each part's name, so the file opens with those names instead of body 1, body 2. A cell with several solids writes name, name 2, …

• Mouse like Bambu Studio: left-drag rotates about the point you pressed on (empty space: about the orbit's centre; exploded, a drag on a part moves it), right-drag or wheel-drag pans, the wheel zooms to the pointer; ⌥-drag on a part slides it along its explode axis. On a trackpad, two fingers turn the model, ⇧ with two fingers pans, pinch zooms to the pointer. A mouse wheel zooms to the pointer: a wheel notch is told from a trackpad's scroll by its size, so a trackpad's scroll is never taken for one (a wheel smoothed into a trackpad's stream, as Mac Mouse Fix's smooth scrolling does, reads as a trackpad). Rotation has no limits; double-click re-centres.

• View cube, lower right: turns with the model, x / y / z axes at its corner. Click a face for that view, an edge or a corner for the view between; the button beside it fits the model.

• Scale reference, the button beside Fit (small, medium and large shapes): shows a thing of known size at its real size, beside the model on its left (the sheet of paper lies centred under it): a US quarter (24.26 mm), a tennis ball (67 mm), a sheet of looseleaf (8½ × 11 in, college ruled, three holes) or a basketball (size 7, 239 mm). The button turns it on and off, its ▾ picks which; Fit takes it in. It is never part of the model: no pick, measure, weight or explode. Kept in this browser.

• Printer build volumes, in the same ▾ menu: a see-through box of the printable width × depth × height, standing on the grid round the model and named at its top: Bambu Lab A1 mini (180³); X1C, P1S… (256³: A1, P1S, P1P, P2S, X1C and X1E, listed in its tip); H2S (340 × 320 × 340); H2D (300 × 320 × 325, what both nozzles reach, as its tip says); Prusa XL (360³). Add a printer… at the bottom takes a name and width × depth × height in mm for one of your own; × removes it. Yours are kept in this browser. Its outline turns red, and the status line says so, when the model does not fit (turned a quarter on the plate counts).

• DXF drawings are paper: drag and scroll pan, two-finger spin turns in 90° steps ([ ] on a keyboard), Flip 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.

• A file opened by path reloads in place when it changes on disk (export again from your CAD; the camera stays).

• ?open=/abs/a.step|/abs/b.stl, ?section=z:0.3, ?explode=0.4 set the viewer from a URL.

These are the defaults. To remap one, right-click, click its key in the menu, then press the new key (⌫ removes it, Esc keeps it). A key another command had swaps over to it. Remaps are yours, kept on your Mac; Reset hotkeys at the bottom of the menu restores the defaults.

Drawing

Press Drawing with a file open. The viewer registers what is on screen and copies a prompt to the clipboard; paste it into Claude Code. Claude calls cadgang_drawing_request, asks the questions a sheet needs one at a time (sheet and orientation, units, which side is the front, which views, scale, the dimensions to place with Measure, title block, notes, parts list), then calls cadgang_drawing_make. The viewer renders the views itself as line art (front, top, right in third angle, an isometric at half scale), draws your dimensions with extension lines and arrows (diameters and radii as leaders), lays out the sheet in the CW&T drawing template — ISO frame with zone grid, 180 × 45 mm title block with the CW&T wordmark, upper-case numbered notes, optional parts list, sheet n/N — and saves <model>.drawing.html next to the model, opened in a new window. ⌘P prints it to PDF at the stated scale.

The template is documented in templates/drawing/README.md; the reference set is templates/drawing/Ultra Bench T Drawing v4.pdf (drawn from a STEP with stepdraw and the spec next to it), which shows every element the template uses: balloons, parts list, sections, schedules.

Live Claude authoring

Open the Cells page while Claude Code builds. The page automatically follows the project folder of the Claude session currently using the CADgang MCP tools, then refreshes after every committed cell change. Claude is instructed to build one reviewable feature or part per cell and evaluate/render it before continuing, so the model appears progressively instead of only after export. The project name in the Cells header shows which session document is on screen.

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.

Softgoods workspace (foundation)

Softgoods are prompt-authored through cadgang_softgoods_get / cadgang_softgoods_set, reviewed in 3D at /softgoods, then exported with cadgang_softgoods_export as one DXF per authoritative pattern plus JSON and printable HTML tech packs. The persistent <project>/cadgang/softgoods.json owns stable point, curve, segment and seam IDs, curved contours, per-edge allowances, notches, grain and arrangement. There is deliberately no manual 2D drafting UI. The 3D review includes an experimental XPBD preview generated from boundary-conforming triangle meshes, with grain-aware warp/weft/bias compliance, seam constraints and fixed attachments in a browser worker. It does not yet have body, panel or self-collision, so it is not a fit guarantee.

REST

ws://…/ws says hello with the server version (pages reload when it changed) and broadcasts markup_changed, snapshot_request, open, drawing and file_changed (a local file opened by path was rewritten).

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, via stepworker.js)
src/core/mesh.js      vertex merge that keeps triangle order, so face ranges stay valid
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
web/cwandt.css        CW&T design system; style.css is the page on top of it
web/drawing.js        the drawing sheet in the CW&T template: line-art views, dimension lines, title block, notes, parts list
templates/drawing/    the drawing template (README) and its reference set, Ultra Bench T Drawing v4.pdf
web/explode.js        explode vectors: along a joint's axis, a shared bore axis, off a mating plane, along a channel, out of a pocket, else radial; no collisions; the order parts come off in
mac/main.swift        WKWebView shell, file associations, Sparkle; build.sh, release.sh, cadgang-open, the icon
test/                 node --test: local-path rules, STEP bodies, DXF entities, explode rules, the icon; explode.harness.mjs runs the solver on a real file

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.