b123d-print

Vibe CAD for 3D printing. Tell your AI assistant what you need, in plain words, with a photo and a few caliper readings. It designs the part, looks at it from every side, checks it for printing problems and hands you a file for your slicer. No CAD skills needed, and it works with any assistant that supports MCP: Claude, Gemini CLI, Cursor, VS Code Copilot, Codex and more.

What you can make

Ask the way you would ask a friend who owns calipers and a CAD program. These were designed this way, and printed:

• "A box for this IR blaster board: the LED pointing out the top, a screw-on lid, two tabs to mount it on the wall." A two-part case, checked against a stand-in of the board so it fits.
• "An outdoor case for this motion sensor. It should slide off a wall plate and keep the rain out." Dovetail rails, a click-in detent, a drain slot, and a cover that prints without supports.
• "An adapter plate: 2-gang box behind, 1-gang smart switch in front." Counterbored screw holes, and a wall check added after the first print broke through a 0.05 mm skin no render showed.

Or remix a model you downloaded (STL, 3MF or STEP) and change it:

• "Here's an L bracket STL I downloaded: turn its two mounting holes into slots and add gussets." The original is loaded as a solid and changed, the checks tell the original's flaws from new ones, and a before/after view shows exactly what moved. (A demo for the docs, not printed yet.)

And the everyday things: a spacer, a knob, a bracket, a cable clip, a replacement for a broken part you can measure. Then keep talking to it: "make it 5 mm taller", "add a hole for an M4 screw", "the lid is too tight". Every dimension stays a named number in a short build123d script, so each change is exact, and you get STEP files to keep editing in other CAD if you want.

Two-part box for an IR transceiver board, with the board stand-ins	Section through the LED: lid cone, board, clearances
Outdoor sensor case: dovetail back plate + support-free cover	Wall plate: section just past the face, where the wall check looks
Remix: a downloaded bracket, before and after	Where the remix differs: red cut, grey added

Documentation: https://kd5ryn.github.io/b123d-print/

Get started in 2 minutes

b123d-print's MCP server is a plug-in that gives your AI assistant CAD tools. It runs on your own computer.

The easy way: paste this into your AI assistant (Claude Code, Claude Desktop, Cursor, Gemini CLI, Codex, …):

Install the b123d-print MCP server for me. It runs with
`uvx --from b123d-print b123d-print-mcp --workspace <folder>`
where <folder> is a folder for my parts, such as ~/parts.
Install uv first if it is missing (https://docs.astral.sh/uv/).
Add the server to your MCP settings, tell me when to restart you,
and after the restart check that its tools (list_parts, new_part,
build_part, ...) are available.

It will probably ask to run a few commands (to install uv and add the server): that is expected.

By hand:

1. Install uv, which fetches Python and everything else b123d-print needs.

2. Add the server. Claude Code:

   claude mcp add b123d-print -- uvx --from b123d-print b123d-print-mcp --workspace ~/parts
   

   Claude Desktop (Settings → Developer → Edit Config):

   {
     "mcpServers": {
       "b123d-print": {
         "command": "uvx",
         "args": ["--from", "b123d-print", "b123d-print-mcp", "--workspace", "/Users/you/parts"]
       }
     }
   }
   

   Cursor, VS Code, Gemini CLI, Codex and others: Connect your MCP client.

3. Restart the assistant.

Then ask: "Design a 40 mm round spacer, 10 mm tall, with an M3 hole." The files land in your parts folder under parts/<name>/out/, ready for your slicer. The first start downloads a few hundred MB and can take a few minutes (Troubleshooting). The assistant checks its work by looking at its renders, so use a client that passes tool images to the model (Claude Desktop and Claude Code do).

Scope: parts for FDM 3D printing, nothing else. Everything is built around a printed part: print orientation with the bed at Z=0, hole compensation, mating clearance, calibration coupons, and print checks built on sourced FDM design rules. It is not a general CAD framework.

What's in it

• b123d-print package + CLI — export, 6-view renders, colored multi-part cross-sections, and print checks: overlap between mating parts, overhang and bridges in print orientation, thin features and wall thickness around cuts, holes (round tops that sag), bed-edge fillets, gaps between moving parts, probes ("is the roof closed?").
• b123d-print-mcp — an MCP server, so it works from Claude Desktop, Claude Code, Gemini CLI, Cursor, VS Code, Codex and other MCP clients. Part scripts are model-written code: they run in a sandbox with a timeout and no network.
• compare — measure a part against a reference STL, 3MF or STEP: size, volume and surface differences, a 0–100 score, pass/fail, and a deviation view (comparing parts).
• Remix — start from someone else's STL, 3MF or STEP: import_model makes a mesh a solid (coplanar triangles merged), the checks tell the original's problems from the ones the remix added, and a before/after view shows the change (remixing a part).
• The workflow, model-neutral — MCP prompts plus an AGENTS.md any agent can read. The rules come from real prints; one exists because a part broke through a 0.05 mm skin that no render showed.
• Examples — four parts designed this way and printed, plus calibration coupons for holes, fits, and overhangs and bridges, in src/b123d_print/examples/.

Advanced: run it on another machine

Not needed for most people. To keep the parts on a home server and design from a laptop, use SSH; for many agents sharing one server (eval runs, a team), HTTP with a named token per tool; for the strongest isolation, or on Windows, Docker. Which mode? compares them.

Documentation

Status

0.x — early. The part-script convention may still change. CI tests macOS and Ubuntu, the built package via uvx, and the Docker image on every push. Windows is untested; Docker is the safe route there.

Credits and license

b123d-print is a thin layer over build123d, Open CASCADE Technology (via OCP), lib3mf, OrcaSlicer's printer data, matplotlib, NumPy, the MCP Python SDK and uv. Details and redistribution notes: THIRD_PARTY.md.

MIT © KD5RYN and contributors.