λ lambdacad-mcp

Let AI draw in your CAD. An MCP server for any AutoLISP-capable CAD — no COM, no SDK, no plugins. Pure AutoLISP. The reference adapter drives BricsCAD on Linux: the first MCP server for a professional DWG CAD on Linux.

"Draw a DN80 flange: front view, hatched section, dimensions — then model it in 3D."

Real-time capture, unedited: front view with bolt circle, hatched section, radial/diameter dimensions, leader, title block — then the same flange modeled as a 3D solid with an AI-written parametric AutoLISP loop and one boolean subtraction. ~20 seconds, 12 tool calls.

Complete 2D drawing, drawn by Claude	3D solids with booleans	Clean render for AI vision

Why this exists

Every other MCP server for a professional DWG CAD (multiCAD-mcp, autocad-mcp, CAD-MCP, ...) talks to the CAD through Windows COM — none of them can run on Linux, and none of them does real 3D.

BricsCAD is the professional DWG CAD that does run natively on Linux. This server drives it through a mechanism that needs no API at all: an AutoLISP file bridge. The MCP server writes LISP expressions to a file, triggers a tiny MCP command inside the CAD, and reads the result back. That's the whole trick — and it unlocks everything the CAD can do, including 3D solid modeling.

Because the bridge is plain AutoLISP + standard DXF entmake + AutoCAD-compatible commands, it is portable by construction: AutoCAD, ARES Commander (also Linux-native!), ZWCAD, GstarCAD and the IntelliCAD family all speak the same language. Porting means swapping the autoload file name and the keystroke trigger — adapters welcome.

MCP client (Claude, Cursor, ...)            BricsCAD (Linux)
        │                                        │
        ▼                                        ▼
  server.py (FastMCP, 100 tools)          c:MCP AutoLISP command
        │        writes LISP  ──►  /tmp/mcp_bricscad.in
        │        triggers via xdotool ──► reads, evals line by line
        │        reads result ◄──  /tmp/mcp_bricscad.out

What it can do

• Full 2D drafting — lines/arcs/polylines/splines, real HATCH (with islands), dimensions incl. radius/diameter/angular, leaders, linetypes (chain/hidden), text styles, trim/extend/fillet/chamfer/offset/mirror/arrays, blocks
• Semantic shapes — slot, bolt_circle, rounded_rect, polygon, center_mark: one call, the server does the math
• 3D solid modeling — box/cylinder/sphere/cone/wedge/torus, extrude/revolve/sweep, union/subtract/intersect, slice — and flatshot_view: auto-generate correct 2D drawing views from the 3D model
• Batch & atomic — draw_batch executes N operations in one round-trip, wrapped in one undo group (one batch = one Ctrl+Z)
• Talk about what the user selected — get_selection reads the GUI pickfirst set; select_by/select_window highlight what the AI found before acting; modify tools accept "selection"
• Verification without screenshots — bounding boxes, key points, exact lengths/areas, intersection checks (collision detection), solid volume/centroid
• Eyes when needed — render_view: BricsCAD's internal PNG render (clean, no UI, ~30 KB) for vision models
• Deliverables — save DWG, export DXF and PDF
• Escape hatch — run_lisp evaluates arbitrary AutoLISP (multi-line, multi-expression): capable models write parametric code and love it

Full reference: docs/TOOLS.md · How it works: docs/ARCHITECTURE.md

Measured, not promised

Metric	Result
Tool calls for a complete dimensioned flange	200 → 22 (9× fewer round-trips vs primitive-per-call)
Trigger latency	0.25 s per call
Error reporting	per-line LISP errors (msg=L2: ...) → models self-correct without screenshots
Exactness	entity_length on an r=20 circle: 125.664 / 1256.637 (2πr, πr² exact)

Details and model-behavior notes (Sonnet writes parametric LISP, Haiku uses typed tools): docs/BENCHMARKS.md

Quick start

Requirements: Linux, BricsCAD (any recent version — tested on V26), Python 3.10+, xdotool.

git clone https://github.com/Psalmustrack/lambdacad-mcp
cd lambdacad-mcp
./install.sh

The installer creates a venv, installs the AutoLISP bridge into BricsCAD's Support/on_doc_load.lsp (idempotent, marker-delimited), and prints ready-to-paste config for Claude Code / Claude Desktop.

Then:

1. Start BricsCAD and open a drawing (the bridge loads when a document opens).
2. Start a new AI session — the bricscad tools appear.
3. Ask: "draw the plan of a 4×3 m room with a door and dimensions".

Configuration (env vars)

Variable	Default	Purpose
BRICS_DISPLAY	session $DISPLAY	X display where BricsCAD runs (e.g. :77 for a nested Xephyr)
BRICS_COMPACT	off	1 = expose only 14 essential tools (~1k schema tokens instead of ~7k) for clients that inject every schema
BRICS_MCP_IN / BRICS_MCP_OUT	/tmp/mcp_bricscad.{in,out}	bridge file paths

Security note

run_lisp and run_command execute arbitrary code inside BricsCAD by design — that's what makes the server fully general. Only connect MCP clients you trust, and treat the bridge files as trusted input. The bridge itself never loads foreign files (read+eval only) and honors BricsCAD's SECURELOAD.

Troubleshooting

Symptom	Fix
ERR: BricsCAD window not found	Is BricsCAD running on BRICS_DISPLAY?
ERR: no response from BricsCAD	Is a drawing open (not the Start page)? The bridge loads on document open.
Commands typed into the drawing as text	Click once inside the drawing area so the command line has focus, then retry.
Wayland	Works via XWayland; if your compositor struggles with heavy CAD redraws, run BricsCAD under a nested X server (Xephyr) and set BRICS_DISPLAY.

Related projects

Project	CAD	Platform	3D
λ lambdacad-mcp (this)	any AutoLISP CAD — BricsCAD reference	Linux	yes
multiCAD-mcp	AutoCAD/BricsCAD/ZWCAD via COM	Windows	no
puran-water/autocad-mcp	AutoCAD LT (LISP bridge)	Windows	no
hvkshetry/autocad-mcp	AutoCAD LT	Windows	no
freecad-mcp (various)	FreeCAD	cross-platform	yes (FreeCAD)

Credit where due: multiCAD-mcp inspired the project; puran-water/autocad-mcp independently validated the LISP-bridge approach on Windows.

Roadmap

• Focus-free dispatch (targeted X synthetic events — no window activation)
• In-process socket bridge (no keystroke trigger, ~0 latency)
• VIEWBASE paper-space drawing views; sheet metal (SMUNFOLD) and BIM commands
• Compact-mode behavioral benchmark

License

Apache 2.0 — with an explicit patent grant and trademark protection for the lambdacad-mcp name.