AutoCAD LT AutoLISP MCP Server

AutoCAD MCP Server

MCP server for AutoCAD LT automation and headless DXF generation.

Two backends, one API:

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/puran-water/autocad-mcp.git
cd autocad-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": {
    "autocad-mcp": {
      "command": "C:\\path\\to\\autocad-mcp\\.venv\\Scripts\\python.exe",
      "args": ["-m", "autocad_mcp"],
      "env": { "AUTOCAD_MCP_BACKEND": "auto" }
    }
  }
}

Key points:

• The command must point to the Windows Python inside the project venv (not WSL python).
• AUTOCAD_MCP_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": {
    "autocad-mcp": {
      "type": "stdio",
      "command": "cmd.exe",
      "args": ["/d", "/s", "/c", "cd /d C:\\path\\to\\autocad-mcp && .venv\\Scripts\\python.exe -m autocad_mcp"],
      "env": { "AUTOCAD_MCP_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

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

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

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 (autocad_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

Note: If you change AUTOCAD_MCP_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.

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 — AUTOCAD_MCP_IPC_TIMEOUT env var (1–300 seconds, default 10).
• Thread-safe backend init — asyncio.Lock prevents parallel initialization races.

License

MIT