sand3d

3D modeling in Python, built for LLMs.

sand3d is a Python library for writing 3D objects as short programs: profiles, solids, edits, frames, joints and assemblies, over Blender's bpy. A program says how a shape is made, part by part and in its own words, so a model writes it in a few hundred tokens and a person can read it.

Website · API for LLMs · Writing an assembly · Export · Citation

Why sand3d

How it is measured, part by part

• Short. A part takes 2 to 6× fewer tokens than the same part in Blender Python, CadQuery or FeatureScript (details).
• The whole API fits in a prompt, about 3,600 tokens (the API).
• Named, not computed. Parts, edges and faces are reached by name, never by hand-computed coordinates.
• Deterministic. The same program builds the same mesh, bit for bit.

A whole object, part by part

A front-loading washing machine in 38 lines of code (play it and read it): the cabinet, the drum, the door with its glass and handle, the detergent drawer and the dial, each a named part, and four joints that say how they move.

door = s3d.group("door", ring, glass, handle)                      # the handle and the glass move with it
s3d.joint("door_hinge", door, hinge, axis="-Z", range=(0, 143))
s3d.joint("drum_spin", drum, front.move(0, 400), kind="continuous")
s3d.joint("drawer_slide", drawer, top_band.move(150), kind="prismatic", axis="+X", range=(0, 200))
s3d.joint("dial_turn", dial, top_band.move(-150), kind="continuous")
return s3d.assembly("washing_machine", cab, drum, door, drawer, dial, front=front)

Export: GLB, URDF, USD, OBJ, STL

One call; the file's extension names the format; lengths in metres.

s3d.export(machine, "washer.glb")    # or .urdf, .usda, .obj, .stl

.usd, .usdc and .usdz come from the .usda through USD's own tools (usdcat, usdzip). The scene is also an ordinary Blender scene, for anything else Blender writes.

Install

Python 3.13 (recommended) or 3.11. Blender comes with it, as the bpy module: 5.2 LTS on Python 3.13, 4.5 LTS on Python 3.11, the two versions the tests run on.

pip install sand3d        # or, in a uv project: uv add sand3d

bpy has no wheel for Python 3.12, nor for Intel Macs from 5.2 on: there, use Python 3.11.

A first program

import sand3d as s3d

def bracket(w=80, d=40, t=6, hole_d=6.6, pitch=50):
    plate = s3d.extrude("plate", s3d.rect(w, d, r=4), t)
    s3d.hole(plate, hole_d, on=s3d.grid(2, 1, pitch, 0))
    s3d.fillet(plate, 1, edges="top")
    return plate

s3d.export(bracket(), "bracket.glb")

Millimetres by default. Every verb with code that runs and its render: the quickstart; objects to play joint by joint: the gallery; every signature: the API. The programs themselves: docs/examples/ and programs/.

Give it to your LLM

Put docs/api.md in the system prompt: the rules of the vocabulary, every signature, and worked examples, in about 3 600 tokens; llms.txt points a model at it. For objects of several parts, the guidelines give the eight rules of an assembly program: the plan first, then the details, then the parts.

What is in it

Everything on one flat s3d.<verb> surface:

No category verbs (chair(), table()): a category is a program written in sand3d.

Citation

If you use sand3d in your work, please cite it. CITATION.cff holds the same, and GitHub shows it as "Cite this repository".

@misc{sand3d2026,
  author = {Neveu, Thibault and Loy, Andr{\'e}a},
  title  = {sand3d},
  year   = {2026},
  note   = {Version 1.6.1},
  url    = {https://github.com/Sandflow-ai/sand3d}
}

Contributing and license

How the library is built, tested and versioned: CONTRIBUTING.md. Apache License 2.0: see LICENSE.