◢ Chisel — AI CAD

Say it. Shape it. Message what you want built; Claude writes a parametric CAD script, it runs in a sandbox, and it appears in a live 3D viewport — exportable to real CAD.

The core idea: the design is a parametric script. Chat edits patch the script; sliders tune its parameters; export emits the geometry. Everything — editing, versioning, parametrics — falls out of that one choice.

Live: https://chisel.theradicalparty.com · pushes to main auto-deploy via the Forgejo post-receive hook.

Architecture (v0 — MVP)

React + react-three-fiber (chat + 3D viewport)
        │  POST /api/generate | /api/repair
        ▼
Hono Worker ── Claude (claude-sonnet-4-6, prompt-cached system prompt)
        │
        ▼  returns a JSCAD script
Sandboxed Web Worker (src/client/engine) ── runs script → binary STL
        ▼
three.js viewport  +  Download STL

• Kernel: JSCAD (@jscad/modeling), pure JS — runs client-side in a Web Worker isolated from the DOM. Exports STL now.
• Agent loop: generate → execute → on error, /api/repair (up to 3×) before the user sees anything.
• Parameters: // @param name default // label comments in the script become live sliders that re-run locally with no API call.

Develop

npm install
wrangler secret put ANTHROPIC_API_KEY   # or add to .dev.vars for local dev
# terminal 1 — Worker API on :8787
npm run dev
# terminal 2 — Vite client on :5173 (proxies /api → :8787)
npm run dev:client

Open http://localhost:5173.

Deploy

npm run deploy        # builds client → ./public, then wrangler deploy

Serves at chisel.theradicalparty.com.

Use your own AI

Two ways to run Chisel on your own model quota instead of the hosted key.

Bring your own key (in the app)

Click the ⚙ gear → paste an Anthropic API key. It's stored only in your browser (localStorage) and sent as x-user-key; the Worker prefers it over the hosted key for generate / repair / verify. Remove it anytime to fall back to the shared key.

MCP server (drive Chisel from your own client)

Chisel is a Model Context Protocol server at https://chisel.theradicalparty.com/mcp (Streamable HTTP, stateless JSON-RPC). Your own client's model writes the build123d script; Chisel validates and exports the real B-rep — so all the language-model cost is on your account.

Tools: build_part (validate/tessellate → triangle count or the traceback to self-repair), export_step (→ STEP file), get_build123d_guide (the full authoring contract). Prompt: write_cad.

Claude.ai (Pro/Max/Team/Enterprise) — Settings → Connectors → Add custom connector → paste the /mcp URL.

Claude Desktop — add to claude_desktop_config.json (remote servers go through the mcp-remote bridge):

{
  "mcpServers": {
    "chisel": {
      "command": "npx",
      "args": ["-y", "mcp-remote", "https://chisel.theradicalparty.com/mcp"]
    }
  }
}

Cursor — add to ~/.cursor/mcp.json:

{
  "mcpServers": {
    "chisel": { "url": "https://chisel.theradicalparty.com/mcp" }
  }
}

Then just ask: "Design an M4 bolt 20mm long with a hex head, build it, and export a STEP." The client will call get_build123d_guide, write a script, build_part to check it (repairing on any traceback), then export_step.

Locking it down (optional). The endpoint is open so anyone can connect. To require a bearer token: wrangler secret put MCP_TOKEN, then have each client send Authorization: Bearer <token> (Claude.ai/Cursor: add it as a custom header; Claude Desktop: mcp-remote … --header "Authorization: Bearer <token>"). Leaving it open keeps the "any user, their own AI" story — locking it makes it private to you.

Roadmap

• v1 — conversational edits as source-of-truth, vision verification (render → "does this match?"), auth + saved projects (D1/R2), 3MF/OBJ export.
• v2 — STEP B-rep engine via build123d/OpenCascade in a Cloudflare Container/Sandbox, so exports reopen cleanly in Fusion/SolidWorks/FreeCAD. Version history & branching.
• v3 — assemblies & mates, dimension queries ("how tall is it?"), manufacturing hints (3D print / CNC).

Layout

src/worker/     Hono API — Claude orchestration, prompts, repair
src/client/     React app, 3D viewer, JSCAD Web Worker engine