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Install Universal Modder in Codex

Quick install

Run the plugin commands in your ordinary terminal:

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

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Before you start

Have Codex installed and authenticated. Plugin support depends on the Codex version and surface you use; check codex --help if the plugin command group is missing.

Read the shared requirements for Git, Python and optional art or video tools. Plugin installation does not supply a model account, a game license or the game's mod loader. The Universal Modder FAQ separates these costs and requirements.

Step-by-step install

Step 1: Identify the terminal environment

sh
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codex --version
codex --help
git --version

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Run these in the same shell that will perform the installation. For WSL, use the tools installed inside WSL. Note the Codex version when recording any installation error.

Step 2: Add the source and install

Run the two quick-install commands, review the repository source and complete any tool approval presented by Codex. Keep the command output if installation fails; a failure to fetch the repository needs different checks from an unknown plugin command.

Step 3: Reopen your project session

Start a fresh Codex session in your mod workspace. Ask it to identify the available mod-any-game skill and the source from which it was loaded. Review the plugin's MCP tools before choosing whether to enable fal asset generation.

Repository alternative

A clone of the repository contains .agents/skills, AGENTS.md and .codex/config.toml:

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

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Review the project's instructions and configuration before trusting the workspace. Keep your mod in its own project or branch so your changes remain distinguishable from the toolkit. If you copy an integration to another directory, verify its discovery paths and MCP setup there instead of assuming the original folder's settings follow it.

Check that it works

Use a read-only agent prompt first:

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Identify the loaded mod-any-game skill and its source.
Run um --help and um --version in your tool shell.
Report the real output and whether the optional fal MCP connection is enabled.
Do not edit game files or call a paid service.

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Then run um --help in your own terminal. If only one environment can find the CLI, follow um command not found. The package declares um version 0.2.0; record the version your install reports.

Your first prompt

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Use Universal Modder to research a game I own: [game, edition and install path].
Search prior field notes, identify the engine and current mod loader,
and propose one small change with a clear in-game success check.
Write MODDING_PLAN.md and record the backup and rollback steps.
Ask for missing paths instead of guessing them.

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Fill in the bracketed details locally. The Universal Modder tutorial develops this into a Terraria weapon workflow, and the examples show what larger projects involve.

Common errors in Codex

  • Unknown plugin command: inspect the version's help and your Codex installation source. Use the repository route if that is the integration your environment supports.
  • Skill is missing: confirm the active project and plugin status, then start a new session. In a clone, confirm .agents/skills is present.
  • CLI is missing: check PATH in the tool environment and install the standalone CLI if necessary.
  • fal connection fails: inspect the MCP status and whether FAL_KEY reaches that process. Start with placeholder art while resolving optional assets.

Uninstall

In the ordinary terminal, remove the installed plugin:

sh
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codex plugin remove universal-modder@universal-modder

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This subcommand is available in codex-cli 0.160.1; on another version, inspect codex plugin --help. To manage marketplaces, follow the Codex plugin documentation. Start a new session and confirm that the plugin is no longer available.

For a clone-only setup, close the workspace and preserve your mod source, notes and backups before removing the clone. If you installed um independently, follow CLI removal.

Other agents

Compare Claude Code, Cursor, Gemini CLI, VS Code / Copilot and OpenCode. The installation overview keeps all six agents and the skills-only route together.

Frequently asked questions

Does Universal Modder support Codex?

Yes. Universal Modder installs as a Codex plugin, and the repository includes Agent Skills files and Codex MCP configuration.

Can I use the skills without a plugin?

Yes. A clone of the repository provides .agents/skills and AGENTS.md. Launch the agent inside that clone, review its configuration and verify skill and tool discovery in the actual session.

Will the plugin give Codex access to my game automatically?

The agent operates within the access and approvals of your environment. Provide the intended game location, review its plan and check each file-changing step.