Build123d

What it does

When your agent uses it

• Creating 3D models
• Exporting to GLB/STEP/STL
• Doing boolean operations (union
• Parametric design

Example prompts

• “/build123d”

Requirements

• Python 3

What it can do on your machine

Read from SKILL.md and the folder at commit 609e888. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  Ships 1 file in scripts/ (Python, from the files we listed), which the agent can run.

  Shell commands in SKILL.md call:

  • uvx
  • bunx
  • curl
  • sh

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  Hosts in commands or code, which the agent is likely to contact:

  • github.com
  • astral.sh

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

Build123d loads about 1.4k tokens when it runs, and up to ~22k if it reads all its reference files. Until then it costs about 130 tokens; SKILL.md has 258 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~130

When it runs · the whole SKILL.md, loaded when a task matches

~1.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~22k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

• NotePipes a well-known installer script into a shellSKILL.md:20

  curl -LsSf https://astral.sh/uv/install.sh | sh

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); the scripts in this folder are not scanned.

SKILL.md

The full file from rawwerks/VibeCAD at commit 609e888, republished under its MIT licence (© rawwerks). 258 words, ~1,391 tokens.

name

build123d

description

CAD modeling with build123d Python library. Use when creating 3D models, exporting to GLB/STEP/STL, or doing boolean operations (union, difference, intersection). Triggers on: CAD, 3D modeling, sphere, box, cylinder, mesh export, GLB, STEP, STL, solid modeling, parametric design, threads, fasteners, bolts, nuts, screws, gears, pipes, flanges, bearings, bd_warehouse, spur gear, helical gear, bevel gear, planetary gear, ring gear, cycloid gear, rack and pinion, gggears, herringbone, gear mesh, gear train.

uvx --from build123d python script.py

curl -LsSf https://astral.sh/uv/install.sh | sh

from build123d import Sphere, Box, Cylinder, export_gltf, export_step, export_stl

#!/usr/bin/env python3
from build123d import Sphere, Box, export_gltf, Pos

# Create shapes
sphere = Sphere(radius=20)
box = Pos(15, 0, 0) * Box(10, 10, 10)

# Boolean union
result = sphere + box

# Export to GLB (for web viewers, Three.js)
export_gltf(result, "./model.glb", binary=True)
print("Exported model.glb")

uvx --from build123d python my_model.py

def inspect(shape):
    bbox = shape.bounding_box()
    print(f"Size: {bbox.max.X - bbox.min.X:.1f} x {bbox.max.Y - bbox.min.Y:.1f} x {bbox.max.Z - bbox.min.Z:.1f}")
    print(f"Volume: {shape.volume:.1f}")
    print(f"Faces: {len(shape.faces())}, Edges: {len(shape.edges())}")

inspect(result)

Box(length, width, height)
Sphere(radius=20)
Cylinder(radius=10, height=25)
Cone(bottom_radius=15, top_radius=5, height=20)
Torus(major_radius=20, minor_radius=5)

union = shape1 + shape2           # Fuse
difference = shape1 - shape2      # Cut
intersection = shape1 & shape2    # Common volume

from build123d import Pos, Rot
moved = Pos(x, y, z) * shape      # Translate
rotated = Rot(rx, ry, rz) * shape # Rotate (degrees)

export_gltf(shape, "./out.glb", binary=True)  # GLB for web
export_step(shape, "./out.step")              # CAD interchange
export_stl(shape, "./out.stl")                # 3D printing

uvx --from build123d python references/examples/01_simple_shapes.py

uvx --from build123d --with bd_warehouse python script.py

uvx --from build123d --with "gggears @ git+https://github.com/GarryBGoode/gggears" python script.py

from gggears import SpurGear, UP
from build123d import export_gltf

gear1 = SpurGear(number_of_teeth=12, module=2.0, height=10.0)
gear2 = SpurGear(number_of_teeth=24, module=2.0, height=10.0)
gear1.mesh_to(gear2, target_dir=UP)

assembly = gear1.build_part() + gear2.build_part()
export_gltf(assembly, "./gears.glb", binary=True)

# 1. Optimize for web delivery (optional)
bunx @gltf-transform/cli optimize model.glb optimized.glb --compress draco

# 2. Render to image for visual verification
bunx render-glb model.glb preview.png

© rawwerks, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 40 other files (scripts, references) in plugins/build123d/skills/build123d of rawwerks/VibeCAD.

• SKILL.md
• references/advanced-patterns.md
• references/bd-warehouse-reference.md
• references/examples/01_simple_shapes.py
• references/examples/02_boolean_operations.py
• references/examples/03_export_formats.py
• references/examples/04_positioning.py
• references/examples/05_sketch_extrude.py
• references/examples/06_fillet_chamfer.py
• references/examples/07_csg_classic.py
• references/examples/08_hole_pattern.py
• references/examples/09_bd_warehouse_threads.py
• references/examples/10_bd_warehouse_fasteners.py
• references/examples/11_bd_warehouse_gears.py
• references/examples/12_bd_warehouse_pipes.py
• references/examples/13_bd_warehouse_flanges.py
• references/examples/14_bd_warehouse_bearings.py
• references/examples/15_gggears_spur.py
• references/examples/16_gggears_helical.py
• … and 22 more

Open the folder on GitHubat commit 609e888