GET STARTED WITH
CODEX.

01 / Before you start

Install Codex first, and make sure you can run a normal session. You also need:

• A PC game you own, in a local install you can inspect.
• Git and Python 3.10+. The upstream project recommends uv for Python tooling.
• ffmpeg for the media workflow. Blender is required when rendering 3D models into sprites.
• A separate test save and a backup of the saves you care about.

Windows games are driven natively or from WSL. A Mac or Linux coding session does not by itself make a Windows game or its mod loader compatible.

02 / Install the toolkit

Use a current Codex CLI with plugin commands. If your version lacks them, use the repository-clone route below.

codex plugin marketplace add rehan-remade/universal-modder
codex plugin add universal-modder@universal-modder

These commands install or open the toolkit. They do not install a game, its community loader, or a finished mod.

Codex marketplace and plugin command syntax is documented in OpenAI’s official developer commands reference .

Prefer to work from a clone?

Open a local clone with your coding agent. The repository includes AGENTS.md and agent-specific configuration. Review that configuration before enabling integrations.

git clone https://github.com/rehan-remade/universal-modder
cd universal-modder

03 / Check the um CLI

Plugin installs and repository clones include the um CLI setup. If um is not on your PATH, or you used the skills-only route, install it separately:

uv tool install git+https://github.com/rehan-remade/universal-modder
um --help

Use um scan --help and um kb --help to see the available inspection and knowledge-base options. If the shell still cannot find um, check your uv tool executable directory and reopen the terminal.

04 / Choose an asset workflow

You can start with placeholder art. For generated images, 3D, audio, and video, upstream uses fal and a fal API key .

export FAL_KEY="your_fal_api_key"

$env:FAL_KEY = "your_fal_api_key"

For local images, um comfy can use an existing ComfyUI server without a fal key. This is an alternative image workflow, not a replacement for every fal media capability.

05 / Verify your setup

Run codex plugin list, then start a new session and ask Codex to find the mod-any-game skill.

Find the mod-any-game skill. Inspect my game installation and search the knowledge base for matching field notes. Tell me the engine, exact version, recommended route, and files you would change. Do not modify anything yet.

Check the response against your installed game. If the agent cannot find a skill, CLI tool, or MCP integration, resolve that setup issue before attempting a mod.

06 / Make one small change

Pick one weapon, one item, or one data change. Have your agent explain the plan, back up saves, implement a minimal version, and test it in the running game.