AutoCAD MCP server

Lets an AI assistant draw in the AutoCAD running on this machine. A small Python server exposes AutoCAD's drawing commands as MCP tools over HTTP; a tunnel makes that reachable by cloud assistants like ChatGPT and Manus.

Built and verified on 2026-07-30 against AutoCAD 2027 (R26.0), Python 3.13.

How it fits together

ChatGPT / Manus  --HTTPS-->  ngrok  -->  127.0.0.1:8770  -->  AutoCAD 2027
                                          server.py           (via COM)

The server talks to AutoCAD through COM, which means AutoCAD has to be running on this machine with a drawing open, and the server has to run as the same Windows user.

Related MCP server: AutoCAD MCP Server

Relationship to the Codex AutoCAD project

There is a second, much larger AutoCAD MCP system on this Desktop under AUTOCAD Codex (C#/.NET, native AutoCAD plug-in, OAuth, per-change approvals). It listens on 8765. This project is deliberately simpler and listens on 8770 so the two can coexist. Only one ngrok agent can run at a time on the free plan, so only one of them can be tunnelled at any moment.

Pick this one when you want an AI to just draw without approving every change. Pick Codex when you want the safety controls.

Setup

pip install -r requirements.txt

Both dependencies were already installed on this machine; the file pins the versions this was verified against.

Running it

1. Open AutoCAD and make sure a drawing is open.

2. Start the server:

powershell -ExecutionPolicy Bypass -File .\run.ps1

It prints its URL, which contains a long random path segment — that path is the password, so the whole URL is a secret. It is generated once and saved to .secret, so restarting the server does not invalidate URLs you already gave to ChatGPT or Manus.

3. Connect the VPN, then open the tunnel in a second window:

powershell -ExecutionPolicy Bypass -File .\start_ngrok.ps1

It prints the full public URL to paste into your AI client.

The VPN is not optional. ngrok refuses agent connections from Iranian IP addresses (ERR_NGROK_9040), and the tunnel dies whenever the VPN drops.

Connecting an AI client

ChatGPT (needs Plus or Pro, web only): Settings → Apps & Connectors → Advanced settings → turn on Developer mode. Back in Apps & Connectors, add a custom connector with the URL from start_ngrok.ps1 and authentication set to No authentication — ChatGPT connectors cannot send a custom header, which is exactly why the secret lives in the URL. In a chat, enable it from the + menu.

Manus: Settings → Connectors → Add connectors → Custom MCP → Direct configuration. Same URL. If you set ACAD_MCP_AUTH_TOKEN, add the header Authorization: Bearer <token> as well.

Claude Code on this machine needs no tunnel at all — point it straight at the local URL:

{ "mcpServers": { "autocad": { "type": "http", "url": "http://127.0.0.1:8770/<secret>/mcp" } } }

What the AI can do

24 tools. Coordinates are drawing units, angles are degrees, everything is 2D at Z=0. Drawing tools return an entity handle, which the query, hatch and erase tools take.

The tool set is deliberately small. Every tool's schema is loaded into the model's context on every single request, so a tool that is rarely the right answer makes the model measurably worse at choosing between the ones that are. Ellipses, point markers, paragraph text and standalone zoom were removed for that reason — draw_batch still accepts mtext and point operations, capture_view zooms to fit on its own, and anything genuinely exotic is one send_command away.

Seeing the drawing

capture_view is what turns this from a one-way pipe into a loop. It plots the current view through AutoCAD's PublishToWeb PNG.pc3 raster plotter, downscales the result with Pillow, and returns it as an actual image in the tool response — so the model looks at the drawing rather than guessing from coordinates.

A typical view costs about 5 KB at 1100 px, which is cheap enough to call after every drawing step. The plot rotation is pinned to zero deliberately; left alone AutoCAD rotates the view to fit the paper and the model then reasons about a sideways drawing. The tool also restores the layout's previous plotter config, so export_pdf keeps working afterwards.

draw_batch matters more than it looks: every tool call is a network round trip to a cloud AI, so drawing a floor plan one line at a time is painfully slow. One batch call draws the lot.

Configuration

All optional, all environment variables.

Security

The honest summary: anyone who has the URL can draw in your AutoCAD and write files into the output folder.

• The secret path is the real gate, because ChatGPT connectors support only OAuth or no authentication and cannot send a token header.

• The server listens on loopback only, so the tunnel is the sole way in.

• File writes are confined to ACAD_MCP_SAVE_DIR; path traversal is stripped.

• send_command is off by default. Turning it on lets a remote AI run arbitrary AutoLISP, which is equivalent to running code on this machine. Leave it off unless you have a specific reason.

• Every tool call is logged to logs/toolcalls.jsonl with its arguments.

• If the URL leaks, delete .secret, restart, and re-paste the new URL.

Unrelated but worth doing: the ngrok authtoken sits in plaintext in C:\Users\zainm\mcp_setup\ngrok.yml. Rotate it at dashboard.ngrok.com.

Testing without any AI

python test_draw.py

Draws a rectangle, circle, arc, text, dimension and hatch straight through the COM bridge — no MCP, no network. If this fails, nothing else will work, and the failure message tells you why.

Troubleshooting

"AutoCAD stayed busy for 10 seconds and refused the request" — AutoCAD is showing a dialog or waiting at the command line. Switch to it, press Escape, close the dialog. The server retries automatically for about 10 seconds first.

"AutoCAD is not running" — open it, with a drawing.

ngrok reports no tunnel — VPN down, or another ngrok agent is already running (the Codex project's one). The free plan allows a single session.

export_pdf says the file is not on disk — background plotting was still running. Check the output folder a moment later.

Port bind fails with WinError 10013 — that port is in a Windows-reserved range. netsh interface ipv4 show excludedportrange protocol=tcp lists them; pick another and set ACAD_MCP_PORT.

Layout

acad.py is the part worth understanding. AutoCAD's COM interface only accepts calls from the thread that initialised COM, and rejects them outright while it is busy, so every tool hands its work to a single dedicated thread that retries with backoff and reconnects if AutoCAD restarts.