build123d-mcp

Give your AI CAD eyes.

build123d-mcp is not a standalone chatbot or CAD program. It is a CAD toolbox that an AI/LLM app can use through MCP.

With an LLM app such as Claude, Cursor, VS Code, Continue, Cline, or Codex CLI, build123d-mcp lets the assistant create build123d CAD models, render previews, measure geometry, fix mistakes, and export files such as STEP, STL, SVG, and DXF. Instead of writing a whole CAD script blindly, the assistant can build a part in small steps and check the result as it goes.

On the public CADGenBench leaderboard in June 2026, using build123d-mcp raised the same model's score from 0.360 to 0.457 and CAD validity from 88% to 100%.

Pick Your Setup

Most users should start with the local MCP server setup:

• You use Claude, Cursor, VS Code, Continue, Cline, or Codex CLI on your own machine.
• Your AI app starts build123d-mcp as a local subprocess.
• You do not need to clone this repository.

Use GitHub Codespaces instead if you want a browser-only trial or a ready-made development workspace with Copilot Chat, Python, uv, and the CAD dependencies already installed.

Use HTTP mode only for advanced deployments where you are hosting the MCP server yourself.

Quick Start

You need:

• uv
• An AI/LLM app that supports MCP, such as Claude Code, Claude Desktop, Cursor, VS Code, Continue, Cline, or Codex CLI

No repository clone is needed for normal use. First check that the package can start:

uv tool run --python 3.12 build123d-mcp@latest --version

Then add the same command to your AI app's MCP config. The common pieces are:

command: uv
args:    ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]

Python 3.11, 3.12, 3.13, and 3.14 are supported. The examples use 3.12 because it is a conservative default, and uv can download it if you do not already have it installed.

Connect To Your AI App

The pieces are:

• The LLM app is where you chat with the assistant.
• MCP is the connection that lets the assistant call tools.
• build123d-mcp is the CAD tool server the assistant calls.

The server normally runs over stdio. Your AI app starts it as a local subprocess when it needs the CAD tools.

Claude Code

Add this to your project's .mcp.json, or to ~/.claude/mcp.json for global use:

{
  "mcpServers": {
    "build123d-mcp": {
      "command": "uv",
      "args": ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]
    }
  }
}

Restart Claude Code after editing.

Claude Desktop

Edit ~/Library/Application Support/Claude/claude_desktop_config.json on macOS, or %APPDATA%\Claude\claude_desktop_config.json on Windows:

{
  "mcpServers": {
    "build123d-mcp": {
      "command": "uv",
      "args": ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]
    }
  }
}

Restart Claude Desktop after saving.

Cursor

Open Settings -> MCP and add a new server entry, or edit ~/.cursor/mcp.json:

{
  "mcpServers": {
    "build123d-mcp": {
      "command": "uv",
      "args": ["tool", "run", "--python", "3.12", "build123d-mcp@latest"]
    }
  }
}

VS Code, Continue, Cline, Codex CLI

Use the same command and arguments in whichever MCP config your AI app or extension reads. The exact file

... View full README on GitHub