MCP+

MCP+ lets AI assistants (Claude Code and other MCP clients) work in your live FreeCAD session: build and inspect models, run Python, drive the GUI the way a user would, and review CAM jobs. It works with FreeCAD 1.1 and newer development builds.

MCP+ is built on spkane's Robust MCP Server and adds:

• CAM tools: path statistics, A/B comparisons between two code trees, geometry finders, test fixtures, posting and G-code diffs, gouge and coverage checks, headless test runs, demo recording.

• GuiDriver: run toolbar commands, fill in task panels, answer modal dialogs by rule (see GuiDriver).

• Runs that outlast their timeout keep going: the answer carries a job_token, and get_output_page reads the rest of the output and the result page by page (after CREATeNG/freecad-mcp-bridge).

• bridge_status: what FreeCAD is busy with, or which modal dialog is blocking it, answered even while every other call would wait (after neka-nat/freecad-mcp).

• execute_python_file: run a script with __file__ set and __name__ == "__main__".

• Safer bridge: every request must carry a per-user token, and requests from foreign web pages are refused (see Security and your data).

• Fixes: Addon Manager crash on install, Qt imports through FreeCAD's PySide wrapper, PartDesign/Sketcher tools on FreeCAD 1.x, screenshots, .env handling.

Install it with the Addon Manager: Edit → Preferences → Addon Manager → Custom repositories → +, add https://github.com/Connor9220/freecad-mcp-plus with branch main, then install MCP+ from Tools → Addon Manager and restart FreeCAD. The MCP server half installs with pip install git+https://github.com/Connor9220/freecad-mcp-plus (command freecad-mcp).

The rest of this README is spkane's original documentation; it still applies, with "Robust MCP Bridge" now shown as "MCP+".

Security and your data

What MCP+ allows. MCP+ lets an AI assistant run any Python code in your FreeCAD session, with your user's permissions, the same as a macro you run yourself. There is no sandbox: the code can read and write your files, start programs and reach the network. Your MCP client is the guardrail: use one you trust, and have it ask for your approval before it runs tool calls.

Who can reach the bridge. The bridge only runs while you start it (auto-start is off unless you turn it on in Edit → Preferences → MCP+). It listens on localhost (ports 9875 and 9876 by default), so other computers can't reach it. Every request must also carry a token:

• On its first start the bridge creates a random token in a file only your user can read: ~/.config/mcp-plus/token on Linux, ~/Library/Application Support/mcp-plus/token on macOS, %APPDATA%\mcp-plus\token on Windows. The MCP server reads the same file, so nothing needs configuring, while other users' programs on the same computer can't get in.

• Edit → Preferences → MCP+ → Security shows the token file, copies the token, or replaces it (takes effect at once). Turning the token off is possible for localhost only, and not recommended.

• Requests sent by web pages in your browser (an Origin other than localhost) are refused.

• To use FreeCAD from another computer, prefer an ssh tunnel to its port. If you do set Listen on to another address, the MCP server there needs the token in FREECAD_AUTH_TOKEN; the bridge never listens beyond localhost without one.

Where your data goes. The add-on and the MCP server collect nothing and send nothing to anyone; there is no telemetry. But whatever the assistant asks FreeCAD for becomes part of its conversation: object names and properties, file names and paths, geometry, the output of code it runs, and screenshots of your 3D view. Your MCP client sends that to your AI provider, under that provider's terms. Don't use MCP+ on designs you aren't allowed to share with your AI provider. Code the assistant runs can also reach the network, as any macro can.

Reporting a security problem. Please use GitHub's private vulnerability reporting (the repository's Security tab) rather than a public issue.

Related MCP server: FreeCAD MCP

Table of Contents

• FreeCAD Robust MCP Server

  • Table of Contents

  • Features

  • Installation Requirements / Dependencies

  • For Users

    • Quick Links

  • Robust MCP Server

    • Installation

      • Using pip (recommended)

      • Using mise and just (from source)

      • Using Docker

    • Configuration

      • Environment Variables

      • Connection Modes

      • MCP Client Configuration

    • Usage

      • Starting the MCP Bridge in FreeCAD

        • Option A: Using the Workbench (Recommended)

        • Option B: Using just commands (from source)

      • Uninstalling the MCP Bridge

        • Checking for Legacy Components

        • Manual Cleanup (if needed)

      • Running Modes

        • XML-RPC Mode (Recommended)

        • Socket Mode (JSON-RPC)

        • Headless Mode

        • Embedded Mode (Linux Only)

    • Available Tools

      • Execution & Debugging (5 tools)

      • Document Management (7 tools)

      • Object Creation - Primitives (8 tools)

      • Object Management (12 tools)

      • PartDesign - Sketching (14 tools)

      • PartDesign - Patterns & Edges (5 tools)

      • View & Display (11 tools)

      • Undo/Redo (3 tools)

      • Export/Import (7 tools)

      • Macro Management (6 tools)

      • Parts Library (2 tools)

  • For Developers

  • Robust MCP Server Development

    • Prerequisites

    • Initial Setup

    • MCP Client Configuration (Development)

    • Development Workflow

    • Running FreeCAD with the MCP Bridge

      • GUI Mode (recommended for development)

      • Headless Mode (for automation/CI)

    • Running Tests

    • Code Quality

  • Architecture

  • Acknowledgements

    • Related Projects

  • License

The macros that were originally in this repo under the /macros directory have been permanently moved to two new GitHub repos:

• spkane/freecad-macro-cut-for-magnets

• spkane/freecad-macro-3d-print-multi-export

FreeCAD Forum: addon discussion post

Features

• 150+ MCP Tools: Comprehensive CAD operations including primitives, PartDesign, booleans, export

• Multiple Connection Modes: XML-RPC (recommended), JSON-RPC socket, or embedded

• GUI & Headless Support: Full modeling in headless mode, plus screenshots/colors in GUI mode

• Macro Development: Create, edit, run, and template FreeCAD macros via MCP

Installation Requirements / Dependencies

• FreeCAD 1.1 or newer

• Python 3.11 (required for FreeCAD ABI compatibility)

For Users

This section covers installation and usage for end users who want to use the Robust MCP Server with AI assistants.

Quick Links

Robust MCP Server

Note: The Linux container and PyPI package are both named freecad-robust-mcp which differs slightly from this git repository name.

Installation

Using pip (recommended)

pip install freecad-robust-mcp

Using mise and just (from source)

git clone https://github.com/spkane/freecad-addon-robust-mcp-server.git
cd freecad-addon-robust-mcp-server

# Install mise via the Official mise installer script (if not already installed)
curl https://mise.run | sh

mise trust
mise install
just setup

Using Docker

Run the Robust MCP Server in a container. This is useful for isolated environments or when you don't want to install Python dependencies on your host.

# Pull from Docker Hub (when published)
docker pull spkane/freecad-robust-mcp

# Or build locally
git clone https://github.com/spkane/freecad-addon-robust-mcp-server.git
cd freecad-addon-robust-mcp-server
docker build -t freecad-robust-mcp .

# Or use just commands (if you have mise/just installed)
just docker::build        # Build for local architecture
just docker::build-multi  # Build multi-arch (amd64 + arm64)

Note: The containerized Robust MCP Server only supports xmlrpc and socket modes since FreeCAD runs on your host machine (not in the container). The container connects to FreeCAD via host.docker.internal.

Configuration

Environment Variables

Connection Modes

Note: Embedded mode crashes on macOS because FreeCAD's FreeCAD.so links to @rpath/libpython3.11.dylib, which conflicts with external Python interpreters. Use xmlrpc or socket mode on macOS and Windows.

MCP Client Configuration

Add something like the following to your MCP client settings. For Claude Code, this is ~/.claude/claude_desktop_config.json or a project .mcp.json file:

{
  "mcpServers": {
    "freecad": {
      "command": "freecad-mcp",
      "env": {
        "FREECAD_MODE": "xmlrpc"
      }
    }
  }
}

If installed from source with mise/uv:

{
  "mcpServers": {
    "freecad": {
      "command": "/path/to/mise/shims/uv",
      "args": ["run", "--project", "/path/to/freecad-addon-robust-mcp-server", "freecad-mcp"],
      "env": {
        "FREECAD_MODE": "xmlrpc"
      }
    }
  }
}

If using Docker:

{
  "mcpServers": {
    "freecad": {
      "command": "docker",
      "args": [
        "run", "--rm", "-i",
        "--add-host=host.docker.internal:host-gateway",
        "-e", "FREECAD_MODE=xmlrpc",
        "-e", "FREECAD_SOCKET_HOST=host.docker.internal",
        "spkane/freecad-robust-mcp"
      ]
    }
  }
}

Docker configuration notes:

• --rm removes the container after it exits

• -i keeps stdin open for MCP communication

• --add-host=host.docker.internal:host-gateway allows the container to connect to FreeCAD on your host (Linux only; macOS/Windows have this built-in)

• FREECAD_SOCKET_HOST=host.docker.internal tells the Robust MCP Server to connect to FreeCAD on your host machine

Usage

Starting the MCP Bridge in FreeCAD

Before your AI assistant can connect, you need to start the MCP bridge inside FreeCAD:

Option A: Using the Workbench (Recommended)

1. Install the Robust MCP Bridge workbench via FreeCAD's Addon Manager:

   • Edit -> Preferences -> Addon Manager

   • Search for "Robust MCP Bridge"

   • Install and restart FreeCAD

2. Start the bridge:

   • Switch to the Robust MCP Bridge workbench

   • Click the Start MCP Bridge button in the toolbar

   • Or use the menu: MCP Bridge -> Start Bridge

3. You should see in the FreeCAD console:

   MCP Bridge started!
     - XML-RPC: localhost:9875
     - Socket: localhost:9876

Option B: Using just commands (from source)

# Start FreeCAD with MCP bridge auto-started
just freecad::run-gui

# Or for headless/automation mode:
just freecad::run-headless

After starting the bridge, start/restart your MCP client (Claude Code, etc.) - it will connect automatically

Uninstalling the MCP Bridge

To uninstall the Robust MCP Bridge workbench:

1. Open FreeCAD

2. Go to Edit -> Preferences -> Addon Manager

3. Find "Robust MCP Bridge" in the list

4. Click Uninstall

5. Restart FreeCAD

Checking for Legacy Components

If you previously used older versions of this project, you may have legacy components installed. Run this command to check what's installed and get cleanup instructions:

just install::status

Manual Cleanup (if needed)

Remove any legacy files that may conflict with the workbench:

# macOS - remove legacy plugin and macro
rm -rf ~/Library/Application\ Support/FreeCAD/Mod/MCPBridge/
rm -f ~/Library/Application\ Support/FreeCAD/Macro/StartMCPBridge.FCMacro

# Linux - remove legacy plugin and macro
rm -rf ~/.local/share/FreeCAD/Mod/MCPBridge/
rm -f ~/.local/share/FreeCAD/Macro/StartMCPBridge.FCMacro

Running Modes

XML-RPC Mode (Recommended)

Connects to a running FreeCAD instance via XML-RPC. Works on all platforms.

FREECAD_MODE=xmlrpc freecad-mcp

Socket Mode (JSON-RPC)

Connects via JSON-RPC socket. Works on all platforms.

FREECAD_MODE=socket freecad-mcp

Headless Mode

Run FreeCAD in console mode without GUI. Useful for automation.

# If installed from source:
just freecad::run-headless

Note: Screenshot and view features are not available in headless mode.

Embedded Mode (Linux Only)

Runs FreeCAD in-process. Only works on Linux - crashes on macOS/Windows.

FREECAD_MODE=embedded freecad-mcp

Available Tools

The Robust MCP Server provides 150+ tools organized into categories. Tools marked with GUI require FreeCAD to be running in GUI mode; they will return an error in headless mode.

Execution & Debugging (8 tools)

Document Management (7 tools)

Object Creation - Primitives (8 tools)

Object Management (12 tools)

PartDesign - Sketching (14 tools)

PartDesign - Patterns & Edges (5 tools)

View & Display (11 tools)

Undo/Redo (3 tools)

Export/Import (7 tools)

Macro Management (6 tools)

Parts Library (2 tools)

CAM review and testing (11 tools)

Tools for reviewing and testing CAM (Path) changes. "Local" tools run on the machine of the MCP server (headless FreeCADCmd, file comparisons) and don't need the bridge.

GUI health (2 tools)

GuiDriver - drive the GUI like a user (6 tools)

The add-on ships guidriver (in freecad/RobustMCPBridge/guidriver/, importable inside FreeCAD as import guidriver; CAM parts in guidriver.cam). It runs real GUI commands, reads and sets task panel widgets through their own Qt API (GUI gating included), presses the task view's OK/Cancel and answers modal dialogs by rule; a dialog no rule matches is rejected after 3 s and reported. See its README.

For Developers

This section covers development setup, contributing, and working with the codebase.

Robust MCP Server Development

Prerequisites

• mise - Tool version manager

• FreeCAD 1.1 or newer

Initial Setup

# Clone the repository
git clone https://github.com/spkane/freecad-addon-robust-mcp-server.git
cd freecad-addon-robust-mcp-server

# Install mise via the Official mise installer script (if not already installed)
curl https://mise.run | sh

# Install all tools (Python 3.11, uv, just, pre-commit)
mise trust
mise install

# Set up the development environment
just setup

This installs:

• Python 3.11 - Required for FreeCAD ABI compatibility

• uv - Fast Python package manager

• just - Command runner for development workflows

• pre-commit - Git hooks for code quality

MCP Client Configuration (Development)

Create a .mcp.json file in the project directory:

{
  "mcpServers": {
    "freecad": {
      "command": "/path/to/mise/shims/uv",
      "args": ["run", "--project", "/path/to/freecad-addon-robust-mcp-server", "freecad-mcp"],
      "env": {
        "FREECAD_MODE": "xmlrpc",
        "FREECAD_SOCKET_HOST": "localhost",
        "FREECAD_XMLRPC_PORT": "9875",
        "PATH": "/path/to/mise/shims:/opt/homebrew/bin:/usr/local/bin:/usr/bin:/bin"
      }
    }
  }
}

Replace the paths with your actual paths:

Finding your mise shims path:

mise where uv | sed 's|/installs/.*|/shims|'
# Example: /home/user/.local/share/mise/shims (on Linux) or ~/.local/share/mise/shims (on macOS)

Development Workflow

Commands are organized into modules. Use just to see top-level commands, or just list-<module> to see module-specific commands.

# Show top-level commands and available modules
just

# Show commands in a specific module
just list-mcp           # Robust MCP Server commands
just list-freecad       # FreeCAD plugin/macro commands
just list-install       # Installation commands
just list-quality       # Code quality commands
just list-testing       # Test commands
just list-docker        # Docker commands
just list-documentation # Documentation commands
just list-dev           # Development utilities

# List ALL commands from all modules
just list-all

# Install/update dependencies
just install::mcp-server

# Run all checks (linting, type checking, tests)
just all

# Quality commands
just quality::lint       # Run ruff linter
just quality::typecheck  # Run mypy type checker
just quality::format     # Format code
just quality::check      # Run all pre-commit hooks

# Testing commands
just testing::unit       # Run unit tests
just testing::cov        # Run tests with coverage
just testing::integration # Run integration tests

# Run the Robust MCP Server (or with debug logging)
just mcp::run
just mcp::run-debug

# Docker commands
just docker::build        # Build image for local architecture
just docker::build-multi  # Build multi-arch image (amd64 + arm64)
just docker::run          # Run container

Running FreeCAD with the MCP Bridge

GUI Mode (recommended for development)

# Start FreeCAD with auto-started bridge
just freecad::run-gui

Headless Mode (for automation/CI)

just freecad::run-headless

Running Tests

# Unit tests only (no FreeCAD required)
just testing::unit

# Unit tests with coverage
just testing::cov

# Integration tests (requires running FreeCAD bridge)
just testing::integration

# Integration tests with automatic FreeCAD startup
just testing::integration-auto

Code Quality

The project uses strict code quality checks via pre-commit:

• Ruff - Linting and formatting

• MyPy - Type checking

• Bandit - Security scanning

• Codespell - Spell checking

• Secrets scanning - Gitleaks, detect-secrets, TruffleHog

# Run all pre-commit hooks
just quality::check

# Run security/secrets scans
just quality::security
just quality::secrets

Architecture

See the detailed architecture document for design documentation covering:

• Module structure

• Bridge communication protocols

• Tool registration patterns

• FreeCAD plugin architecture

Acknowledgements

MCP+ is a copy of spkane/freecad-addon-robust-mcp-server by Sean P. Kane, extended by Billy Huddleston. It also takes ideas from neka-nat/freecad-mcp (bridge status, version check) and CREATeNG/freecad-mcp-bridge (paged output for long runs, Origin check, running files). All three are MIT licensed; their notices are in LICENSE.

spkane's original acknowledgements:

This project was developed after analyzing several existing FreeCAD Robust MCP implementations. We are grateful to these projects for their pioneering work and the ideas they contributed to the FreeCAD + AI ecosystem:

Related Projects

• neka-nat/freecad-mcp (MIT License) - The queue-based thread safety pattern and XML-RPC protocol design (port 9875) were directly inspired by this project. Our implementation maintains protocol compatibility while being a complete rewrite with additional features.

• jango-blockchained/mcp-freecad - Inspired our connection recovery mechanisms and multi-mode architecture approach.

• contextform/freecad-mcp - Informed our comprehensive PartDesign and Part workbench tool coverage.

• ATOI-Ming/FreeCAD-MCP - Inspired our macro development toolkit including templates, validation, and automatic imports.

• bonninr/freecad_mcp - Influenced our simple socket-based communication approach.

See docs/COMPARISON.md for a detailed analysis of these implementations and the design decisions they informed.

License

MIT License - see LICENSE for details.