Greenloom CAD MCP Server

MCP server for AutoCAD LT automation and headless DXF generation.

Two backends, one API:

Backend	Runtime	Requires AutoCAD?	Screenshot
File IPC	Windows Python	Yes — AutoCAD LT 2024+ (Windows)	Win32 PrintWindow
ezdxf	Any platform	No (headless)	matplotlib render

The server exposes 8 consolidated tools (drawing, entity, layer, block, annotation, pid, view, system) over the MCP stdio transport. An MCP client (Claude Desktop, Claude Code, etc.) connects and drives AutoCAD through natural-language requests.

Prerequisites (File IPC backend)

• Windows 10/11 (the File IPC backend uses Win32 APIs for focus-free window messaging)
• AutoCAD LT 2024 or newer — AutoLISP support was added in LT 2024 for Windows. AutoCAD LT for Mac exists but does not support AutoLISP.
• Python 3.10+ (Windows native — not WSL Python)
• uv package manager (install guide)

The ezdxf headless backend works on any platform (Linux, macOS, WSL) for offline DXF generation without AutoCAD installed.

Quick Start

1. Clone and install

git clone https://github.com/Greenmint-labs/greenloom_CAD_MCP.git
cd greenloom_CAD_MCP
uv sync

2. Load the LISP dispatcher in AutoCAD LT

Open AutoCAD LT and load mcp_dispatch.lsp using APPLOAD:

1. Type APPLOAD in the AutoCAD command line
2. Browse to <repo>/lisp-code/mcp_dispatch.lsp
3. Click Load
4. You should see: === MCP Dispatch v3.1 loaded === and Ready for commands via (c:mcp-dispatch)

Tip: Add the file to your AutoCAD Startup Suite (in the APPLOAD dialog) so it loads automatically with every drawing.

3. Configure your MCP client

Add to your MCP client configuration (e.g. Claude Desktop claude_desktop_config.json):

{
  "mcpServers": {
    "greenloom-cad-mcp": {
      "command": "C:\\path\\to\\greenloom-cad-mcp\\.venv\\Scripts\\python.exe",
      "args": ["-m", "greenloom_cad_mcp"],
      "env": { "GREENLOOM_CAD_BACKEND": "auto" }
    }
  }
}

Key points:

• The command must point to the Windows Python inside the project venv (not WSL python).
• GREENLOOM_CAD_BACKEND can be auto (default — tries File IPC, falls back to ezdxf), file_ipc (requires AutoCAD), or ezdxf (headless only).

Running from WSL

If your MCP client runs in WSL (e.g. Claude Code), launch the server through cmd.exe so it runs as a native Windows process:

{
  "mcpServers": {
    "greenloom-cad-mcp": {
      "type": "stdio",
      "command": "cmd.exe",
      "args": ["/d", "/s", "/c", "cd /d C:\\path\\to\\greenloom-cad-mcp && .venv\\Scripts\\python.exe -m greenloom_cad_mcp"],
      "env": { "GREENLOOM_CAD_BACKEND": "auto" }
    }
  }
}

4. Verify

From your MCP client, call:

system(operation="status")

You should see backend: "file_ipc" if AutoCAD is running, or backend: "ezdxf" for headless mode.

Tools

drawing — File/drawing management

Operation	Description	File IPC	ezdxf
create	Reset to clean drawing (erase all + purge)	Yes	Yes
open	Open an existing drawing	Yes	Yes (DXF)
info	Get entity count and layers	Yes	Yes
save	Save current drawing (to path if given)	Yes	Yes
save_as_dxf	Export as DXF	Yes	Yes
plot_pdf	Plot to PDF	Yes	No
purge	Purge unused objects	Yes	Yes
get_variables	Get system variables by name	Yes	Yes
undo	Undo last operation	Yes	No
redo	Redo last undone operation	Yes	No

entity — Entity CRUD + modification

Create: create_line, create_circle, create_polyline, create_rectangle, create_arc, create_ellipse, create_mtext, create_hatch

Read: list, count, get

Modify: copy, move, rotate, scale, mirror, offset*, array, fillet*, chamfer*, erase

* offset, fillet, chamfer are File IPC only (not supported in ezdxf headless backend).

layer — Layer management

list, create, set_current, set_properties, freeze, thaw, lock, unlock

block — Block operations

Operation	File IPC	ezdxf
list	Yes	Yes
insert	Yes	Yes
insert_with_attributes	Yes	Yes
get_attributes	Yes	Yes
update_attribute	Yes	Yes
define	No	Yes

annotation — Text, dimensions, leaders

create_text, create_dimension_linear, create_dimension_aligned, create_dimension_angular, create_dimension_radius, create_leader

pid — P&ID operations (CTO symbol library)

setup_layers, insert_symbol, list_symbols, draw_process_line, connect_equipment, add_flow_arrow, add_equipment_tag, add_line_number, insert_valve, insert_instrument, insert_pump, insert_tank

P&ID symbol insertion requires the CAD Tools Online (CTO) P&ID Symbol Library installed at C:\PIDv4-CTO\. The ezdxf backend has built-in CTO library support. For the File IPC backend, some P&ID operations require additional LISP helpers — see the P&ID section in the wiki for setup details.

view — Viewport and screenshot

Operation	Description
zoom_extents	Zoom to show all entities
zoom_window	Zoom to a specified window
get_screenshot	Capture current AutoCAD view as PNG

Screenshots use PrintWindow (Win32) for the File IPC backend — works even when AutoCAD is minimized or in the background. The ezdxf backend renders via matplotlib.

system — Server management

status, health, get_backend, runtime, init, execute_lisp

execute_lisp runs arbitrary AutoLISP code (File IPC only). Pass data: {code: "(+ 1 2)"}. This turns the server into an extensible automation platform — any valid AutoLISP expression can be executed.

Architecture

MCP Client (Claude)
    │  stdio (JSON-RPC)
    ▼
Python MCP Server (greenloom_cad_mcp)
    │
    ├── File IPC Backend ──► C:/temp/*.json ──► mcp_dispatch.lsp (AutoCAD LT)
    │   PostMessageW(WM_CHAR) to MDIClient — no focus steal
    │
    └── ezdxf Backend ──► in-memory DXF (headless, no AutoCAD needed)

The File IPC backend sends keystrokes to AutoCAD's MDIClient window via PostMessageW(WM_CHAR), triggering the (c:mcp-dispatch) AutoLISP command. This approach does not steal window focus — you can continue working in other applications while automation runs.

Environment Variables

Variable	Default	Description
GREENLOOM_CAD_BACKEND	auto	Backend selection: auto, file_ipc, ezdxf
GREENLOOM_CAD_IPC_DIR	C:/temp	Directory for IPC command/result JSON files (must match on both Python and LISP sides)
GREENLOOM_CAD_IPC_TIMEOUT	10.0	IPC command timeout in seconds (1-300)
GREENLOOM_CAD_ONLY_TEXT	false	Disable screenshot capture (text feedback only)

Note: If you change GREENLOOM_CAD_IPC_DIR, you must also update the *mcp-ipc-dir* variable in mcp_dispatch.lsp to match.

Development

uv sync
uv run pytest tests/ -v

AutoCAD LT AutoLISP Compatibility

AutoLISP was added to AutoCAD LT in the 2024 release (Windows only). AutoCAD LT for Mac does not support AutoLISP.

Supported (LT 2024+ Windows)	Not Supported
.lsp / .fas / .vlx / .dcl	VLIDE (Visual LISP IDE)
All vl-* utility functions	vlax-* (ActiveX/COM)
File I/O (open, read-line, etc.)	Express Tools
Entity access (entget, entmod, etc.)	3D operations
Selection sets	AutoLISP on Mac

The mcp_dispatch.lsp dispatcher is fully compatible with LT 2024+.

What's New in v3.1

• execute_lisp — Run arbitrary AutoLISP code via temp file pattern. Turns the server from a fixed command set into an extensible automation platform.
• Undo / Redo — Single-step undo and redo via drawing tool.
• Drawing open — Open existing .dwg files programmatically (FILEDIA suppressed).
• Drawing create — Now resets current drawing (erase all + purge) instead of _.NEW, preserving the LISP dispatcher namespace.
• Drawing save with path — save with a path parameter uses SAVEAS; without path uses QSAVE.
• get_variables fix — Respects the names parameter; returns requested variables with proper type handling.
• Polyline/leader fix — Point arrays properly encoded via semicolon-delimited format.
• ESC prefix — Sends 2x ESC before each dispatch to cancel stale pending commands from prior timeouts.
• UTF-8/cp1252 fallback — Handles non-ASCII characters in LISP result files (AutoCAD writes Windows-1252).
• Configurable IPC timeout — GREENLOOM_CAD_IPC_TIMEOUT env var (1–300 seconds, default 10).
• Thread-safe backend init — asyncio.Lock prevents parallel initialization races.

License

MIT