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Agent skill

Forgecad Verify Mujoco

by ForgeCAD in ForgeCAD/forgecad-public-kit

Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready.

MITAuto-check passedDevelopment

Install Forgecad Verify Mujoco

skills CLI
$ npx skills add ForgeCAD/forgecad-public-kit --skill forgecad-verify-mujoco -a claude-code

Project install by default; add -g for ~/.claude/skills/.

GitHub CLI
$ gh skill install ForgeCAD/forgecad-public-kit forgecad-verify-mujoco --agent claude-code

Project scope by default; add --scope user for a personal install. Needs GitHub CLI 2.90.0 or later (public preview).

Manual copy
$ git clone --depth 1 https://github.com/ForgeCAD/forgecad-public-kit.git skills-src && mkdir -p .claude/skills && cp -r skills-src/skills/forgecad-verify-mujoco .claude/skills/forgecad-verify-mujoco && rm -rf skills-src

Use ~/.claude/skills/ instead of .claude/skills for a personal install. The folder must contain SKILL.md.

Claude Code skills documentation · loads skills from .claude/skills/

Facts

Skill name
forgecad-verify-mujoco
GitHub stars
941
Token cost
~1.6k tokens
SKILL.md length
814 words
Files
2 (incl. scripts)
Skills in repo
10
Repo updated
First seen
Licence
MIT

At a glance

Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready.

  • Works in 8 steps: Export from the exact source file. → Load the generated scene in MuJoCo. Use… → Check the root behavior. If the model… → …
  • Development work in your project
  • SKILL.md covers Definition Of Done, Helper Script, Contact Debugging Rules and Reporting
  • Runs Python scripts from its folder; calls uv and python

What it does

Forgecad Verify Mujoco is an agent skill from ForgeCAD/forgecad-public-kit. Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready.

Its SKILL.md is about 1.6k tokens, which your agent loads only when the skill is triggered. The skill folder holds 2 other files, including scripts (for example `scripts/mujoco_verify.py`).

It sits in Development. The repository describes itself as: Public companion kit for ForgeCAD: examples, agent skills, docs links, and issue tracking. The hosted CAD app and core source live elsewhere. The licence is MIT.

When your agent uses it

  • Development work in your project

Example prompts

  • “/forgecad-verify-mujoco”

Requirements

  • Python 3

Workflow steps

8 steps, taken from the first numbered list in SKILL.md.

  1. Export from the exact source file.
  2. Load the generated scene in MuJoCo. Use scene.xml, not only the model XML, so the floor/camera/package context is included.
  3. Check the root behavior. If the model has a free root, it needs real support/contact geometry or an explicit fixed-root export path. Do…
  4. Check initial poses numerically. For mechanisms, compute the expected body/link axes from the design source and compare them to MuJoCo…
  5. Keep meaningful collisions. Do not mark moving functional parts Sim.collider.none(...) just to make motion pass. If full visual mesh…
  6. Run the intended control with numeric acceptance criteria. Define the expected signed post-settle joint travel before running the test…
  7. Inspect contact pairs. Contact names should match the physical story: floor/support, card/card, wheel/ground, stop/follower, etc. Contacts…
  8. Render evidence. Save initial, settled, and driven frames from views that actually show the moving parts. If the model orientation is not…

What it can do on your machine

Read from SKILL.md and the folder at commit 7523f68. 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), which the agent can run.

    Shell commands in SKILL.md call:

    • uv
    • python

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

  • Network

    No URLs in SKILL.md. Its commands use uv, which can reach the network depending on how they are called.

    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

Forgecad Verify Mujoco loads about 1.6k tokens when it runs. Until then it costs about 42 tokens; SKILL.md has 814 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it
~42
When it runs · the whole SKILL.md, loaded when a task matches
~1.6k

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

Auto-check passed

The automated check found no risky patterns in SKILL.md.

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 ForgeCAD/forgecad-public-kit at commit 7523f68, republished under its MIT licence (© ForgeCAD). 814 words, ~1,620 tokens.

Download SKILL.mdSave it as .claude/skills/forgecad-verify-mujoco/SKILL.md (or your agent's skills folder). This skill also uses 1 other file; get the full folder from GitHub.
name
forgecad-verify-mujoco
description
Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready.
forgecad-public
true

Verify MuJoCo

Use this when forgecad export mjcf ... is part of the deliverable. A model is not sim-ready just because forgecad check simready passes or the MJCF file loads: it must be loaded in MuJoCo, stepped under gravity, driven with the intended controls, contact pairs inspected, and rendered from useful views.

Routing: geometry-only visual inspection -> forgecad-inspect-model; model authoring/API questions -> forgecad; building a new model -> forgecad-build-model.

Definition Of Done

  1. Export from the exact source file.
    bash
    rm -rf /tmp/forgecad-mjcf && mkdir -p /tmp/forgecad-mjcf
forgecad export mjcf path/to/model.forge.js --output /tmp/forgecad-mjcf
  2. Load the generated scene in MuJoCo. Use scene.xml, not only the model XML, so the floor/camera/package context is included.
  3. Check the root behavior. If the model has a free root, it needs real support/contact geometry or an explicit fixed-root export path. Do not hide a floor failure by turning the whole shell into a giant bounding box that blocks moving internals.
  4. Check initial poses numerically. For mechanisms, compute the expected body/link axes from the design source and compare them to MuJoCo xmat/xpos. Joint ref/default and connector frames can disagree with visual intuition.
  5. Keep meaningful collisions. Do not mark moving functional parts Sim.collider.none(...) just to make motion pass. If full visual mesh contact is unstable, use a physically defensible simplified collider or proxy and state what physical surface it represents.
  6. Run the intended control with numeric acceptance criteria. Define the expected signed post-settle joint travel before running the test: e.g. "this drive should rotate the drum -0.04 to -0.06 cycles, then stop near zero velocity" or "this wheel should move at least +1 cycle and keep spinning". Use cycles for revolute/indexing mechanisms when that is easier to reason about, and radians for direct MuJoCo qpos checks. A controller that only jitters, moves the wrong direction, overshoots through a stop, or eventually jams after skipping the intended state is a failure even when the process exits 0.
  7. Inspect contact pairs. Contact names should match the physical story: floor/support, card/card, wheel/ground, stop/follower, etc. Contacts against a filled-in AABB, hidden fixture, or unrelated side plate usually indicate bad collider selection.
  8. Render evidence. Save initial, settled, and driven frames from views that actually show the moving parts. If the model orientation is not obvious, generate a labeled camera preview grid first, inspect it, then rerun with the azimuth/elevation that shows the functional face. Do not report GIFs/frames before visually confirming they are not from the back, underside, or an occluded side.
Show full SKILL.md (416 more words)Show less

Helper Script

This skill ships a MuJoCo smoke verifier:

bash
uv run --python 3.11 --with mujoco --with pillow \
  python <this-skill-dir>/scripts/mujoco_verify.py /tmp/forgecad-mjcf \
  --settle-seconds 2 \
  --seconds 8 \
  --actuator drum_velocity=-0.75 \
  --watch-joint drum_joint \
  --expect-drive-cycles drum_joint=-0.06:-0.03 \
  --expect-final-qvel drum_joint=-0.02:0.02 \
  --render-dir /tmp/forgecad-mjcf/verify \
  --camera-preview-grid

Use --actuator name=value more than once for multi-actuator models. Use --expect-drive-cycles joint=min:max to assert signed final-minus-settled revolute travel in cycles/turns. Use --expect-drive-delta joint=min:max when you want raw MuJoCo qpos units instead. Use --expect-final-qvel joint=min:max to assert terminal velocity when the mechanism should stop or continue at a bounded speed. The script prints JSON with root drift, initial-to-final joint delta, post-settle drive delta, derived cycle counts, final velocities, expectation ranges, and top contact pairs, then writes PNG frames if --render-dir is supplied.

Prefer explicit travel envelopes over loose "it moved" checks:

  • Stops/latches: assert a signed drive cycle or delta range and a near-zero final velocity range.
  • Continuous drives: assert the signed drive cycle/delta is large enough over the run and final velocity remains in the expected direction/range.
  • Indexing mechanisms: assert the expected cycle step size, not just eventual stall. If the mechanism reaches a stop only after skipping several indices, treat that as failure.
  • Gravity-settling mechanisms: evaluate functional travel with post-settle drive delta, not initial-to-final delta.

When rendered orientation matters, start with --camera-preview-grid, open camera_preview_grid.png, pick the azimuth that shows the mechanism face or contact interface, then rerun with --camera-azimuth <deg> and any needed --camera-lookat, --camera-distance, or --camera-elevation adjustment. For mechanism evidence, prefer front/front-quarter views for user-facing GIFs and add a side/contact view only when it explains a collision better.

Contact Debugging Rules

  • In MuJoCo UI, enable contact visualization with Rendering -> Contact points and Contact forces; use the right-side perturb/visualization panels if available in your build.
  • If rotation is blocked, list contacts during the stall and sort by repeated pairs. The blocker is usually the pair that appears every step while the driven joint velocity trends to zero.
  • If a body falls through the floor, inspect the exported geoms. Visual geoms have contype="0" conaffinity="0" and cannot support anything; collision geoms are usually group 3.
  • Bounding boxes are fast but dangerous for hollow frames, windows, handles, and side plates. They collide as the filled AABB, not the visible object.
  • Mesh collision on complex moving parts can be too exact or solver-hostile. Prefer simple physical proxies for contact-critical moving bodies, such as a slab for a flap card or cylinders for rolling contact, but keep them colliding.

Reporting

Report the exact export command, the MuJoCo command/script, key numeric results, the most important contact pairs, and the rendered image paths. Say what was not verified. Never say "sim-ready" when only forgecad run, forgecad check simready, or a successful export was executed.

© ForgeCAD, 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 1 other file (scripts) in skills/forgecad-verify-mujoco of ForgeCAD/forgecad-public-kit.

  • SKILL.md
  • scripts/mujoco_verify.py

Open the folder on GitHubat commit 7523f68

Compare with similar skills

Forgecad Verify Mujoco next to the 5 skills that share the most tags, products or categories with it. Stars are the repository's; “used in” counts other GitHub owners with a copy.

Forgecad Verify Mujoco compared with similar skills
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PR Babysitteropeninterpreter/openinterpreter69k3 repos~4.2kAutomated safety check: PassApache-2.0
Code Review ChecklistshareAI-lab/learn-claude-code78k5 repos~1.1kAutomated safety check: PassMIT

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Categories

Questions about Forgecad Verify Mujoco

What does Forgecad Verify Mujoco do?

Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready. Forgecad Verify Mujoco is an agent skill from ForgeCAD/forgecad-public-kit. Verify a ForgeCAD MJCF export in MuJoCo with dynamics, contacts, controls, joint travel, and rendered evidence before calling it simulation-ready.

When should I use Forgecad Verify Mujoco?

Forgecad Verify Mujoco fits situations like: development work in your project.

How do I install Forgecad Verify Mujoco in Claude Code?

Run `npx skills add ForgeCAD/forgecad-public-kit --skill forgecad-verify-mujoco -a claude-code`. Or copy the skill folder (skills/forgecad-verify-mujoco in ForgeCAD/forgecad-public-kit) into .claude/skills/forgecad-verify-mujoco in your project. Claude Code loads it when a task matches its description.

How do I install Forgecad Verify Mujoco in Codex?

Run `npx skills add ForgeCAD/forgecad-public-kit --skill forgecad-verify-mujoco -a codex`. Or copy the skill folder (skills/forgecad-verify-mujoco in ForgeCAD/forgecad-public-kit) into .agents/skills/forgecad-verify-mujoco in your project. Codex loads it when a task matches its description.

Can I use Forgecad Verify Mujoco in Cursor, Gemini CLI or GitHub Copilot?

Cursor, Gemini CLI, GitHub Copilot and OpenCode also load SKILL.md folders. With the skills CLI, run `npx skills add ForgeCAD/forgecad-public-kit --skill forgecad-verify-mujoco -a cursor` (or -a gemini-cli, github-copilot or opencode for the others). To copy it by hand, put the folder in .cursor/skills/forgecad-verify-mujoco, .gemini/skills/forgecad-verify-mujoco, .github/skills/forgecad-verify-mujoco and .opencode/skills/forgecad-verify-mujoco in your project.

What does Forgecad Verify Mujoco need to run?

Going by SKILL.md and its folder, Forgecad Verify Mujoco needs Python for the scripts in its folder and the command-line tools its instructions call (uv and python). Our summary lists: Python 3.

Does Forgecad Verify Mujoco access the network?

SKILL.md contains no URLs. Its commands use uv, which can reach the network depending on how they are called. This is read from the text; nothing was executed.

Is Forgecad Verify Mujoco safe to install?

Our automated static check of SKILL.md found no risky patterns, such as piping downloads into a shell, reading credential files or hidden Unicode. It is not a guarantee. The check reads SKILL.md only: the scripts in the folder are not scanned, so read them before running anything.

What licence does Forgecad Verify Mujoco use?

Forgecad Verify Mujoco is published under the MIT licence (the repository's licence). It allows redistribution, so the full SKILL.md is shown on this page.

How many tokens does Forgecad Verify Mujoco use?

About 1.6k tokens (SKILL.md is roughly 6.5k characters). Agents keep only the skill's name and description in context until a task matches; then they load SKILL.md in full.

What are the alternatives to Forgecad Verify Mujoco?

Skills that share tags, products or a category with Forgecad Verify Mujoco: Vercel Composition Patterns (supabase/supabase, 111k stars), Finishing a Development Branch (obra/superpowers, 297k stars), Typescript Advanced Types (rolling-scopes/rsschool-app, 10k stars) and PR Babysitter (openinterpreter/openinterpreter, 69k stars). The comparison table on this page puts their stars, adoption, token cost, safety result and licence side by side.

Who maintains Forgecad Verify Mujoco?

ForgeCAD (a GitHub organization) maintains it in ForgeCAD/forgecad-public-kit, which has 941 GitHub stars. The repository holds 10 skills in this directory. The repository was last updated on June 15, 2026.

Source: ForgeCAD/forgecad-public-kit on GitHub. Facts on this page come from the repository at the commit we read; the author's words are quoted as theirs.