CAD modeling and inspection

Provenance: maintained in earthtojake/text-to-cad. Use the installed local skill files for the current interface.

Start with the task

Read only the references needed for the request.

Task	First action	Reference
Create or edit a part or assembly	Find the existing Python model, or create a decorated model below; edit source and run python <model>.py.	Model contract, shape construction; positioning for assemblies
Organize a CAD project	Follow its existing layout; for a new multi-model project use src/, format output folders, and a model catalog.	Project layout, minimal starters
Export STL, 3MF or GLB	Add a mesh decorator for a maintained output, or run the format's build INPUT.step OUT command for a one-off export.	Mesh exports
Resolve a reference from a prompt	Identify its saved STEP/STP document, open it with read_scene, and call scene.resolve(ref) as shown below.	Reference syntax and inspection
Measure or check geometry	Write a Python check using native build123d geometry and, where useful, cadgen.geometry.	Inspection and validation
Model from an image or drawing	Extract the specified dimensions and record meaningful assumptions.	Interpreting the request
Review appearance or motion	Snapshot the saved document; use declared kinematics or animation for poses and clips.	Snapshots, kinematics
Diagnose a failure	Read the error and check the relevant model, geometry or command contract.	Repair loop, version migration

For 2D DXF drawings use $dxf; this skill owns any 3D part the drawing projects. Use the corresponding robot-description skill for URDF, SRDF or SDF.

Setup and paths

Install this skill's requirements.txt with the active project interpreter. Rendering also needs Chromium:

python -m pip install -r /path/to/installed/cad/requirements.txt
python -m playwright install chromium

Treat python in examples as the active interpreter. cadgen doctor <skill-dir> checks the skill's package pin and CAD kernel; use it for installation or OCP load errors. python -m cadgen.cli is the PATH-independent equivalent of cadgen. Use the relevant subcommand's --help for additional flags.

Run project commands from the CAD project root. CLI input/output paths and read_scene/read_step paths are working-directory-relative; decorator out= paths are relative to the model script. Anchor file inputs on __file__ when the model must run from any directory.

Create or edit a model

A model is a plain Python script with a parameterless decorated function returning a build123d shape. Use one model per entrypoint, with the script and its declared outputs sharing a filename stem. For example, src/bracket.py:

from cadgen import build123d as bd
from cadgen import step

WIDTH = 40.0


@step(out="../STEP/bracket.step")
def bracket():
    body = bd.Box(WIDTH, 20, 6)
    body.label = "bracket"
    return body


if __name__ == "__main__":
    bracket()

python src/bracket.py

• Edit the model source when it exists, then run it to regenerate its outputs. Document export and snapshot commands take saved files and never run source.
• Keep meaningful dimensions explicit. Use millimeters and XY/+Z unless the task or project specifies another convention; choose a useful functional datum. Prefer closed, positive-volume solids for physical parts, while honoring requests for surfaces or construction geometry.
• Put parameterized geometry in ordinary factory functions; a decorated model selects a configuration. Keep module bodies cheap: create geometry and read CAD inputs inside the model or its helpers. Use the lazy bd import above; use postponed annotations when annotations mention bd types.
• Call child models inside the assembly model. Place their results with .moved() or Location * shape to preserve shared geometry. Use meaningful occurrence labels and source-defined placements. Rerun the parent assembly to incorporate a changed child.
• Read vendor STEP inputs with cadgen.read_step; it records the file as a build input. Declare other data inputs with cadgen.declare_input. Never read a model's own output as its input. Geometry must not depend on untracked time, random values, environment variables or the working directory.
• When named purchasable parts are needed, search $step-parts before making placeholders. Record an unsuccessful search and any placeholder assumptions.

For unfamiliar dimensions or interfaces, record the assumptions needed to model and verify them. Ask for missing information when it materially affects the requested result. Inspection and export requests do not need a modeling brief.

Mesh exports

Stack @stl, @threemf or @glb on the model for outputs that should be maintained on every run. A model may declare only meshes; STEP is optional. For a one-off export from an existing generated or imported STEP:

cadgen stl build STEP/bracket.step STL/bracket.stl
cadgen 3mf build STEP/bracket.step 3MF/bracket.3mf
cadgen glb build STEP/bracket.step GLB/bracket.glb

Omitting OUT writes one sibling file with the requested extension. It does not discover declared model variants. See mesh exports for decorator examples, mesh tolerances and animated GLB.

Prompt references and inspection

A reference such as assembly.step#o1.2.f7 identifies geometry in a particular saved document. Use the prompt's file context to select that document:

from cadgen import read_scene

scene = read_scene("STEP/assembly.step")
selection = scene.resolve("assembly.step#o1.2.f7")
face = selection.shape()  # owned native geometry, in document world coordinates
print(selection.ref, face.area)

For a bare #o1.2.f7, use the identified target file. For a model-script prefix, find its declared STEP output and resolve the #... portion there. Do not guess between ambiguous files or labels. Numeric refs belong to that saved revision; reopen and reselect after rebuilding. The inspection reference covers label aliases, enumeration, measurements and small reusable operations.

There is no inspect CLI. Put exploratory checks in the project's ignored tmp/ (or system /tmp/); retain reusable checks in checks/ or its existing test directory. Keep them outside model-source and raw-output folders.

Verify and hand off

Choose checks from the requested dimensions, clearances and topology. For STEP outputs, check the saved artifact with read_scene or read_step. For mesh-only models, check the model's returned native geometry and review the mesh output; do not add a STEP solely to satisfy the workflow. Report units, thresholds, selected geometry and untested requirements. A failed computation is not a pass.

After creating or visibly changing geometry, generate and review at least one snapshot of the resulting STEP or mesh. Choose additional views to expose the features under review; see snapshot policy and options.

cadgen step snapshot STEP/bracket.step tmp/review.png
cadgen stl snapshot STL/bracket.stl tmp/mesh.png

Repair failures in the source and rerun the affected checks. Use geometry and images for CAD comparisons; path-targeted git status is bookkeeping, not geometric evidence. cadgen store why <model>.py explains unexpected rebuilds; python <model>.py --force forces one model, and cadgen daemon status shows build progress. More diagnostics are in the model contract.

For created or modified STEP/STP, STL, 3MF and GLB files, hand their explicit paths to $cad-viewer when installed and include its returned live links. If unavailable or startup fails, report that and use geometry checks and snapshots. Include output files, reviewed PNGs, checks actually run, and material assumptions or limitations in the final response. Explain any snapshot skip or failure using the cases in the snapshot reference.