partforge

AI-built parametric CAD for 3D printing. Describe a part to an AI agent and get a forge — a self-contained web app for that one part: a 3-D viewer, a control panel with just the parameters that matter, and STL / STEP / 3MF export. Share the forge and anyone can dial in their own version and print it.

A forge isn't a frozen STL. It's open-source code that renders and regenerates the model live, so the part stays editable — resize it for a different bearing, screw, or motor without relearning a heavy CAD tool — and anyone (or their own agent) can read the source and extend it.

partforge is the engine behind the forge: a small npm framework that an LLM tuned for tool use can drive to author, test, and measure a part, then ship it as a browser app.

See it

• Live showcase — https://scottsykora.github.io/partforge/ — example forges (Faceted Planter, Spacer, Filleted Box) you can open, adjust, and export.
• A real forge — https://scottsykora.github.io/Drum-Machine/ — a parametric capstan drum built with partforge for a robotics project.

Build your own forge

You don't write CAD by hand. Point a tool-using AI agent (Claude Code, or the Claude / ChatGPT desktop apps with file access) at this repo and describe what you want:

Using the partforge framework at https://github.com/scottsykora/partforge, build me a <your part> — <the dimensions, fits, and features that matter>.

Expect a few turns. The first attempt is often rough, but you refine it in plain language — "make the bore fit an M3", "add a 2 mm fillet", "thinner walls", "taller by 10" — until the part is right. You end up with a forge you can host anywhere and hand to anyone.

How it works

You — or an agent — write one part definition: geometry build functions plus a parameter schema. partforge renders everything else: the 3-D viewer, the control panel, the geometry workers, and the export buttons. Each control can carry a description, a preset, or be hidden, so the interface stays simple while the part stays deeply adjustable.

Two geometry backends run in Web Workers, and partforge routes each part to whichever it needs:

• Manifold — fast preview meshes and STL / 3MF.
• Replicad (OpenCASCADE-in-WebAssembly) — exact B-rep for STEP export and native fillet / chamfer.

The viewer is three.js.

Because a part is just code, an agent can build it and check its own work: the partforge/testing helpers measure volume and bounding box, probe geometry, detect self-overlap between sub-parts, and render the model so a multimodal agent can see what it made. A part can also declare a verify block — a manufacturing (DFM) profile plus design-intent assertions — that flags problems like a too-thin wall or a part that won't fit the print bed before anyone hits export.

Requires a Vite-based app. partforge is published as plain ESM source and relies on Vite's worker / WASM / CSS import handling.

Install

npm install partforge

Use

// app.js
import { mount } from "partforge";
import part from "./parts/my-part.js";
mount(part, {
  createWorker: (name) =>
    new Worker(new URL("./part-worker.js", import.meta.url), { type: "module", name }),
});

// part-worker.js
import { runWorker } from "partforge/worker";
import part from "./parts/my-part.js";
runWorker(part);

Test your parts headlessly with partforge/testing (bootManifoldKernel, bootOcctKernel, assemblyOverlaps, measure, verify, meshVolume, bboxSize).

Smoke-test that an app actually boots (real Chromium, real worker/WASM): npm run check (or node scripts/check-app.mjs <entry>.html) — it loads the app and verifies the kernel boots with no errors. Needs Playwright: npm i -D playwright && npx playwright install chromium.

Authoring guide

docs/AUTHORING-PARTS.md is the full guide — the part contract, the geometry kernel API, the parameter schema, app wiring, testing, and gotchas. See Designing the control panel in that guide for how to write descriptions, hide internal params, and keep the interface simple while staying deeply adjustable. src/parts/demo.js is a minimal worked example; src/parts/planter.js is a richer one (facets, taper, twist, even walls, an optional feature, and a verify block).

Locally, npm run dev then open /demo.html, /planter.html, or /filleted-box.html.

• Agent clarification (request-a-pick): an external tool can ask the user to click geometry and get the Selection back — serve with ?pickserver, drive with partforge pick-serve + partforge pick "<prompt>" …. See skills/partforge/SKILL.md and the authoring guide.

License

MIT