PromptCAD

How it works

Five stages, and none of them are “generate a mesh”

The hard part of language-driven CAD is not producing a shape — it is producing a shape you can still edit afterwards, with the dimensions you actually asked for. PromptCAD is built around that.

1. You describe the part

   Plain English, in the panel. Three ways to work: Structured for a whole part at once, Engineering to add one operation at a time and watch each step land, and Python when you would rather write the script yourself.

2. The model returns a plan, not code

   The answer has to be a list of CAD operations drawn from a fixed vocabulary of 19, each with typed and validated parameters. That constraint is what makes the result editable instead of a one-shot blob.

   Local models are held to it by a GBNF grammar, so malformed output is not merely rejected — it cannot be produced. Cloud models use their structured-output modes.

3. PromptCAD builds a parametric feature tree

   Each operation becomes a real FreeCAD object. A plate with a bored hole and filleted edges is a box, a cylinder, a cut and a fillet — four nodes in the tree, each with editable properties. Change the box's width and everything downstream rebuilds.

4. It measures what it built

   After building, PromptCAD inspects the actual solid: bounding box, volume, and a measurement table per feature. Then it reads the dimensions back out of your prompt and compares them with the geometry. Ask for 60 mm and get 6 mm, and it says so rather than handing you a confident wrong part.

5. It repairs its own mistakes, within limits

   When an operation fails or a check does not pass, the error goes back to the model and it tries again — under a fixed repair budget with a loop guard. It gives up and tells you, rather than spinning.

The full vocabulary — solids, booleans, patterns and edge treatments:

• box
• cylinder
• sphere
• cone
• torus
• extrude
• revolve
• cut
• fuse
• common
• linear_pattern
• polar_pattern
• mirror
• shell
• hole
• fillet
• chamfer
• translate
• rotate

The window

Minimal by default, complete when you want it

PromptCAD is built on FreeCAD, which opens with nine toolbars and roughly eighty icons. That is the right default for a CAD program you drive with a mouse and the wrong one for a CAD program you drive by describing things — the prompt ends up a narrow strip beside a wall of buttons it does not need.

So PromptCAD starts with one short toolbar row and gives the prompt real width. Nothing has been removed: one button — or Ctrl+Shift+T — brings the entire FreeCAD toolset back, and it remembers which way you like it.

• DefaultOne toolbar row, six icons: new, open, save, the prompt panel, settings, and the toggle. Nine toolbars hidden.
• All toolsEvery FreeCAD toolbar and workbench back, one click or Ctrl+Shift+T away.

Models

Bring your own model. It finds it by itself.

PromptCAD ships without weights, so the download stays small and you are never locked to one vendor's model. Download a model and PromptCAD picks it up — there is no settings dialog to hunt through and no path to paste.

1. Install PromptCAD

   One installer, including the inference engine. Nothing downloads behind your back later.

2. Download a model

   Click a button below. Your browser saves it to Downloads — that is fine, leave it exactly there.

3. Start PromptCAD

   It finds the file, selects it, and lists it in the dropdown at the top of the panel.

Runs on your machine

Quantised GGUF builds. As a rule of thumb the download size is roughly the memory the model needs while running.

Too big for a workstation

These are genuinely open-weights models and also far larger than any desktop will hold. They are listed because PromptCAD can use them — through an API provider such as OpenRouter — not because you should download the weights.

Or use an API, if you would rather

Local is the default because your geometry stays yours. But PromptCAD speaks to seven providers, and model lists are fetched live from each one rather than hardcoded — so a model released this morning is selectable this afternoon.

• Local (GGUF, offline)
• Ollama / LM Studio
• Anthropic (Claude)
• OpenAI
• Google Gemini
• xAI (Grok)
• OpenRouter

Getting the part out

Because the result is real B-rep geometry rather than a mesh, it exports as real geometry.

• STEPExact B-rep for CAD and CAM interchange. Curves stay curves — nothing is faceted on the way out.
• STLFor printing and preview, with the mesh tolerance under your control.
• 3D print modeGive it your build volume and PromptCAD checks the part against it, and can scale to fit.
• TemplatesSave a part you like as a template and start the next one from it.

Where PromptCAD looks for models

Any of these. Drop a file in one and it is found on the next start.

%USERPROFILE%\Downloads
<install folder>\models
%APPDATA%\PromptCAD\<version>\models
%USERPROFILE%\.lmstudio\models
%USERPROFILE%\.machine\models

Requirements

• SystemWindows 10 or 11, 64-bit.
• DiskAbout 2.5 GB installed, plus whatever your model needs.
• Memory8 GB for the recommended 4B model; 16 GB for 12B.
• GPUStrongly recommended for local models. They will run on the CPU alone, but at minutes per part rather than seconds.
• NetworkOnly to download PromptCAD and a model. After that it works offline.

Licensing

PromptCAD is built on FreeCAD, redistributed unmodified under the LGPL-2.1-or-later, and includes llama.cpp under the MIT License. PromptCAD's own code is MIT. The full notices and a written offer for source ship in the application's legal folder.

FreeCAD is a trademark of the FreeCAD Project Association. PromptCAD is an independent project, not affiliated with or endorsed by them — please report PromptCAD problems to PromptCAD.

No model weights are distributed with PromptCAD. Each model above is published by its own authors under its own licence, and that licence governs your use of it.