ldraw-mcp

Give your MCP client eyes for LEGO® models.

Render LDraw files (.ldr / .mpd / .dat) to images with real part geometry — studs, slopes, window glass — using headless Blender and the ImportLDraw addon. The output looks like a BrickLink Stud.io render, with no GUI anywhere in the loop.

_{A ~90-line .ldr rendered front-left and rear-right — actual bricks, not a geometric proxy.}

Point a vision-capable model at a build and it sees the actual bricks: crossed rotation matrices, floating plates, sunken windows — the kinds of export bugs a geometric proxy render will happily hide.

Quickstart

# 1. install
pip install ldraw-mcp

# 2. install the LDraw parts library + ImportLDraw addon
ldraw-mcp-setup

# 3. register with Claude Code
claude mcp add ldraw -- ldraw-mcp

Then ask things like "render output/build.ldr and tell me what looks wrong" — the model sees the render, not just the text.

Blender is a prerequisite (see Requirements); it is not installed by ldraw-mcp-setup.

Tools

azimuths is a comma-separated list of view angles in degrees; each is rendered and the views are stitched horizontally. Elevation is fixed at 22°. Higher samples = cleaner but slower.

A part the LDraw library does not have cannot be drawn. The render tools still return the picture of the rest, followed by a text block that names each file the importer could not find. When every file is found, the image comes alone.

The render tools and bill_of_materials follow the same references. Files next to the model (sub.ldr, models/wheel.ldr) and library parts are followed. A reference that could leave the folder it is looked up in (.., an absolute path, a drive, ~), or a file in the model's folder that links outside it, is refused with the same message by every tool. Inline text follows the same rule.

The three query tools are read-only and need no Blender. bill_of_materials expands MPD sub-models (and sibling .ldr/.mpd files next to the model) with their multiplicity, and resolves colour 16 to the colour of the referencing line; colour 24 (edge) is reported as 24. It counts without a parts library — descriptions and colour names are then null. A colour code LDConfig.ldr does not define is listed under unknown_color_codes, a part the library lacks under parts_not_in_library; neither is dropped. A sub-model reference cycle is an error that names the cycle. lookup_color and search_parts need the library (ldraw-mcp-setup).

Requirements

• Blender 4.x on PATH, or point LDRAW_MCP_BLENDER at the binary. Install it yourself (package manager, blender.org, or a local build); ldraw-mcp-setup does not install Blender.
• ImportLDraw addon (io_scene_importldraw) in Blender's addons dir — installed by ldraw-mcp-setup.
• LDraw parts library at ~/.ldraw (or LDRAW_LIBRARY_PATH) — installed by ldraw-mcp-setup.

Environment variables

Manual setup

If ldraw-mcp-setup can't detect things automatically:

• LDraw library: download complete.zip and unzip so that ~/.ldraw/parts/ exists.
• ImportLDraw addon: download the latest release from TobyLobster/ImportLDraw and install it via Blender > Preferences > Add-ons > Install, or unzip into ~/.config/blender/<version>/scripts/addons/io_scene_importldraw/. (Launch Blender once first so the config directory exists.)

Troubleshooting

• check_renderer says NOT FOUND: run ldraw-mcp-setup, or set the relevant env var above.
• No GPU / WSL2 / containers: rendering uses Cycles on CPU, which works headless everywhere — no GPU or display needed. A ~150-part model takes a few seconds at the default 640px / 24 samples.
• "no mesh objects imported": the addon couldn't resolve parts — usually a wrong or incomplete LDraw library path. Re-run setup or check LDRAW_LIBRARY_PATH.
• Addon not enabled: the render script enables it automatically per run; if a manual Blender session complains, enable io_scene_importldraw in Preferences > Add-ons.

Provenance

This renderer was extracted from the prompt2brick project, where it started life as the vision critic's "see the actual model" path. prompt2brick keeps its own vendored copy of the render wrapper and Blender script, but this repo is the canonical source going forward — fixes and improvements to the renderer should land here first and be ported back into prompt2brick.

License

MIT — see LICENSE.

_{LEGO® is a trademark of the LEGO Group, which does not sponsor, authorize, or endorse this project. This tool is not affiliated with the LEGO Group, BrickLink, or the LDraw.org organization.}