urdf

What the source does

• FilesystemNone observedNo reads or writes in the source
• NetworkNone observedNo outbound calls in the source
• ShellNone observedNo commands run in the source
• DependenciesPinnedNothing floats
• SecretsNone foundNo keys in source

Five audit layers

Gates applied: no behavioural pass.

Audit 0.4.1 · source sha 3ad82be902e3 · 29 Oct 2026Report an issue or request a re-scan

• Publisherearthtojake GitHub userOwner of the repository this skill is read from
• Source folderearthtojake/text-to-cad/skills/urdfThe exact folder we audited
• LicenceMITAs the repository states it
• Commit pinned for this verdict3ad82be902e3A new audit runs when the source changes
• Repository statusNot archivedPushed today
• Sandboxed runNot runSkills are read, not executed; layer L4 is skipped

Its description: URDF robot description authoring and validation. Use when creating, editing, inspecting, validating, or debugging `.urdf` files, robot links, joints, limits, inertials, visual/collision geometry, mesh references, frame…

---
name: urdf
description: URDF robot description authoring and validation. Use when creating, editing, inspecting, validating, or debugging `.urdf` files, robot links, joints, limits, inertials, visual/collision geometry, mesh references, frame conventions, or robot-description artifacts. Use the SRDF skill for MoveIt2 semantic groups and IK/path-planning semantics; use the CAD skill for STEP/STL/3MF/DXF/GLB outputs. Open and visually review existing URDF files in CAD Viewer.
license: MIT
---

# URDF

Provenance: maintained in [earthtojake/text-to-cad](https://github.com/earthtojake/text-to-cad).
Use the installed local skill files as the runtime source of truth; the
repository link is only for provenance and release review.

Use this skill for URDF robot-description outputs. Treat URDF work as constrained kinematic modeling, not just XML writing. The main correctness risks are frame placement, joint-axis semantics, unit consistency, mesh scale, and inertial data.

## Setup

Run cadgen through the `cadgen` command its installation writes, so this skill's commands
share one installation, and its engine server, with the CAD app's:

- `cadgen` below means `cadgen +0.8.2` (`~/.local/bin/cadgen +0.8.2` where `~/.local/bin` is not on your PATH)
- `python` below means `cadgen +0.8.2 run`

If `cadgen` is not on your PATH, or it says 0.8.2 is not installed, run
`uvx --no-config --managed-python --python 3.13 --from cadgen==0.8.2 cadgen doctor` once,
outside any sandbox or with its permission: it installs cadgen, registers it, writes the
`cadgen` command and starts the engine. With the CAD app's server running, nothing else
needs the sandbox's permission: it starts the engine and holds it. Without it, a sandboxed
shell cannot start the engine; when a command says no engine is running, run `cadgen server`
outside the sandbox once.

## Core Rules

1. The `.urdf` file is the source of truth. Author and edit URDF XML directly; do not build a Python generation pipeline for it.
2. Before writing or changing URDF XML, establish the robot's frame, joint, geometry, unit, and assumption ledger and embed it as a comment block at the top of the `.urdf` file. See `references/design-ledger.md`.
3. Use URDF frame semantics exactly. Joint origins, link frames, joint axes, and visual/collision/inertial origins use different reference frames. See `references/frame-semantics.md`.
4. Do not infer spatial transforms, mesh units, handedness, axes, or joint signs from vague prose. Use CAD transforms, dimensioned drawings, measured values, existing source data, or explicit documented assumptions.
5. Never freehand numeric values that are the result of computation — inertia tensors, centers of mass, unit conversions across many links, mirrored transforms. Compute them: closed-form formulas for primitives, or a throwaway helper script for mesh-derived values. See `references/inertials.md`.
6. For physical links, model `inertial`, `visual`, and `collision` separately when the target consumer needs them. Frame-only links may intentionally omit mass and geometry.
7. Validate every created or modified `.urdf` with `cadgen urdf validate` before reporting completion. See `references/validation.md`.
8. Helper scripts are allowed and encouraged for computation, but they are scaffolding, not the artifact's source of truth. For complex or genuinely parametric models it is reasonable to keep a model-local helper script on disk next to related source code (for example STEP generator sources) and note it in the ledger; this is optional, and the checked-in `.urdf` remains canonical.

## Show the model

Show the user each model you create or change, and any model or file they ask to see.
A file you export is a download: give its path, do not open it.
Snapshots and validation don't replace this. Never screenshot the viewer to confirm your
own work; review with `cadgen snapshot`.

- If your tools include `cad_show` (your host may prefix it), call it with the model's id
  or the file's absolute path, and follow its description for when to call it again.
  The other tools depend on the host. A host that draws CAD cards or tabs (Claude
  Desktop, the Codex app) also has `cad_view`, which reads what the user selected, and
  `cad_screenshot`, which shows you what they see, both of a card or tab that is open, for
  when they ask about it. A text host (Claude Code in a terminal, `codex exec`) draws
  nothing: its `cad_show` opens the model's page in the user's browser and answers with
  the URL to give them, and it has no view to read. `cad_inspect`, `cad_snapshot` and
  `cad_export` are on every host. Call only the tools you have, and never say a card
  shows a model when your host drew none.
- Otherwise give the user the page's link once: a model's page is the `view:` line its
  run prints. For a file, run the CAD Viewer, from any folder:

  ```bash
  cadgen viewer --json FILE [FILE ...]
  ```

  The command ensures this installation's engine, registers each file and prints
  its page, `/<id>`, then exits. Read each file's `url` from `documents` in its one
  JSON line (never guess the port); the URL carries its token query. A page follows
  every later run of its model and every rewrite of its file, so share it once.
  Return that link to the user. If it fails to launch, say so.

A `.urdf` you write is the robot's model, not an export: show it. Review mesh scale
and placement, then sweep every movable joint against the
design ledger. A link alone does not complete the [viewer sweep](references/validation.md);
report any checks you could not perform.

## Workflow

1. Identify the target `.urdf` file and its consumers: RViz, robot_state_publisher, Gazebo/Ignition, MoveIt, a real robot driver, or another simulator.
2. Read or create the design ledger before editing frames, origins, axes, mesh scale, limits, or inertials. Keep the ledger as a comment block in the `.urdf` itself.
3. Prepare mesh assets first when links reference meshes: one mesh p

Excerpt, first 6,000 characters of SKILL.md, verbatim from the audited commit. It is text from someone else’s repository, quoted so you can judge it before your agent reads it.

1. 2026-10-29
   ✓SAFE B 89 / 100

   first audit · source 3ad82be902e3

Questions about urdf

• github.com/earthtojake/text-to-cad/tree/main/skills/urdf — the audited source at commit 3ad82be902e3 and every finding aboveObserved · 29 Oct 2026

Spotted something wrong? Report a correction · Methodology