UnrealCodex

OpenAI Codex CLI integration for Unreal Engine 5.7 - Get AI coding assistance directly in the editor with built-in UE5.7 documentation context.

Language: English | 한국어

Supported Platforms: Windows (Win64), Linux, and macOS (Apple Silicon). Codex CLI on Windows is still less battle-tested than Linux/macOS.

Overview

UnrealCodex integrates the OpenAI Codex CLI directly into the Unreal Engine 5.7 Editor. Instead of using the API directly, this plugin shells out to the codex command-line tool, leveraging your existing Codex authentication and capabilities.

Key Features:

• Native Editor Integration - Chat panel docked in your editor with live streaming responses, tool call grouping, and code block rendering
• MCP Server - 20+ Model Context Protocol tools for actor manipulation, Blueprint editing, level management, materials, input, and more
• Dynamic UE 5.7 Context System - The MCP bridge includes a dynamic context loader that provides accurate UE 5.7 API documentation on demand
• Blueprint Editing - Create and modify Blueprints, Animation Blueprints, and state machines (still experimental, so verify results before relying on them)
• Level Management - Open, create, and manage levels and map templates programmatically
• Asset Management - Search assets, query dependencies and referencers
• Async Task Queue - Long-running operations won't timeout
• Script Execution - Codex can write, compile (via Live Coding), and execute scripts with your permission
• Session Persistence - Conversation history saved across editor sessions
• Project-Aware - Automatically gathers project context such as modules, plugins, assets, and editor viewport state
• Uses Codex Authentication - No separate API key management is required

Prerequisites

1. Install Codex CLI

npm i -g @openai/codex

2. Authenticate Codex CLI

codex login

This opens an authentication flow for your ChatGPT/Codex account (or API key mode if configured).

3. Verify Installation

codex --version
codex exec --skip-git-repo-check "Reply with OK"

Installation

(Check the Editor category in the plugin browser. You may need to scroll down if search does not surface it.)

Step 1: Clone and Build

This plugin must be built from source for your platform and engine version. No prebuilt binaries are included.

1. Clone this repository (includes the MCP bridge submodule):

   git clone --recurse-submodules https://github.com/online5880/UnrealCodex.git

   If you already cloned without --recurse-submodules, run:

   cd UnrealCodex
   git submodule update --init

2. Build the plugin:

   Windows:

   Engine\Build\BatchFiles\RunUAT.bat BuildPlugin -Plugin="PATH\TO\UnrealCodex\UnrealCodex\UnrealCodex.uplugin" -Package="OUTPUT\PATH" -TargetPlatforms=Win64

   Linux:

   Engine/Build/BatchFiles/RunUAT.sh BuildPlugin -Plugin="/path/to/UnrealCodex/UnrealCodex/UnrealCodex.uplugin" -Package="/output/path" -TargetPlatforms=Linux

   macOS:

   Engine/Build/BatchFiles/RunUAT.sh BuildPlugin -Plugin="/path/to/UnrealCodex/UnrealCodex/UnrealCodex.uplugin" -Package="/output/path" -TargetPlatforms=Mac

Step 2: Install the Plugin

Copy the built plugin to either your project or engine plugins folder.

Option A: Project Plugin (Recommended)

Copy the build output to your project's Plugins directory:

YourProject/
├── Content/
├── Source/
└── Plugins/
    └── UnrealCodex/
        ├── Binaries/
        ├── Source/
        ├── Resources/
        ├── Config/
        └── UnrealCodex.uplugin

Option B: Engine Plugin (All Projects)

Copy to your engine's plugins folder:

Windows:

C:\Program Files\Epic Games\UE_5.7\Engine\Plugins\Marketplace\UnrealCodex\

Linux:

/path/to/UnrealEngine/Engine/Plugins/Marketplace/UnrealCodex/

Step 3: Install MCP Bridge Dependencies

Required for Blueprint tools and editor integration:

cd <PluginPath>/UnrealCodex/Resources/mcp-bridge
npm install

Step 4: Launch

Launch the editor - the plugin will load automatically.

macOS Quick Start (Apple Silicon)

For full details, see INSTALL_MAC.md.

1. Install Node.js and Codex CLI:

   brew install node
   npm i -g @openai/codex
   codex login

2. Install the plugin into your project's Plugins/ directory
3. Install MCP bridge dependencies:

   cd YourProject/Plugins/UnrealCodex/Resources/mcp-bridge
   npm install

4. Launch the editor and open Tools > Codex Assistant

Linux Quick Start (Rocky/Fedora)

For full details, see INSTALL_LINUX.md.

1. Install Libraries:

   sudo dnf install -y nss nspr mesa-libgbm libXcomposite libXdamage libXrandr alsa-lib pciutils-libs libXcursor atk at-spi2-atk pango cairo gdk-pixbuf2 gtk3

2. Install Clipboard Support:

   sudo dnf install -y wl-clipboard   # Wayland
   sudo dnf install -y xclip          # X11 fallback

3. Setup Wayland:

   export SDL_VIDEODRIVER=wayland
   export UE_Linux_EnableWaylandNative=1

4. Build and Launch:

   ./UnrealEditor -vulkan

Usage

Opening the Codex Panel

Menu -> Tools -> Codex Assistant

Example Prompts

How do I create a custom Actor Component in C++?

What's the best way to implement a health system using GAS?

Explain World Partition and how to set up streaming for an open world.

Write a BlueprintCallable function that spawns particles at a location.

How do I properly use TObjectPtr<> vs raw pointers in UE5.7?

Input Shortcuts

Shortcut	Action
Enter	Send message
Shift+Enter	New line in input
Escape	Cancel current request

Features

Session Persistence

Conversations are automatically saved to your project's Saved/UnrealCodex/ directory and restored when you reopen the editor. The plugin maintains conversation context across sessions.

Project Context

UnrealCodex automatically gathers information about your project:

• Source modules and their dependencies
• Enabled plugins
• Project settings
• Recent assets
• Custom CLAUDE.md instructions

MCP Server

The plugin includes a Model Context Protocol (MCP) server with 20+ tools that expose editor functionality to Codex and external tools. The MCP server runs on port 3000 by default and starts automatically when the editor loads.

Tool Categories:

• Actor Tools - Spawn, move, delete, inspect, and set properties on actors
• Level Management - Open levels, create new levels from templates, list available templates
• Blueprint Tools - Create and modify Blueprints (variables, functions, nodes, pins)
• Animation Blueprint Tools - Full state machine editing (states, transitions, conditions, batch operations)
• Asset Tools - Search assets, query dependencies and referencers with pagination
• Character Tools - Character configuration, movement settings, and data queries
• Material Tools - Material and material instance operations
• Enhanced Input Tools - Input action and mapping context management
• Utility Tools - Console commands, output log, viewport capture, script execution
• Async Task Queue - Background execution for long-running operations

For full MCP tool documentation with parameters, examples, and API details, see UnrealCodex MCP Bridge.

Dynamic UE 5.7 Context System

The MCP bridge includes a dynamic context loader that provides accurate UE 5.7 API documentation on demand. Use unreal_get_ue_context to query by category (animation, blueprint, slate, actor, assets, replication) or search by keywords. Context status is shown in unreal_status output.

Configuration

Custom System Prompts

You can extend the built-in UE5.7 context by creating a CLAUDE.md file in your project root. Starter templates are available at UnrealCodex/CLAUDE.md.default and UnrealCodex/CODEX.md.default:

# My Project Context

## Architecture
- This is a multiplayer survival game
- Using Dedicated Server model
- GAS for all abilities

## Coding Standards
- Always use UPROPERTY for Blueprint access
- Prefix interfaces with I (IInteractable)
- Use GameplayTags for ability identification

Allowed Tools

By default, the plugin runs Codex with these tools available through its runtime policy. You can adjust runtime/tool behavior in UnrealCodex/Source/UnrealCodex/Private/CodexSubsystem.cpp and UnrealCodex/Source/UnrealCodex/Private/CodexCodeRunner.cpp.

MCP Server IDs

Codex examples use the MCP server ID unrealcodex.

Config.AllowedTools = { TEXT("Read"), TEXT("Grep"), TEXT("Glob") }; // Read-only

How It Works

1. User enters a prompt in the editor widget
2. Plugin builds context from UE5.7 knowledge + project information
3. Executes Codex non-interactively via codex exec with JSON event streaming
4. Codex runs with your project as the working directory
5. Response is captured and displayed in the chat panel
6. Conversation is persisted for future sessions

Command Line Equivalent

cd "C:\YourProject"
codex exec --json --skip-git-repo-check \
  "How do I create a custom GameMode?"

Troubleshooting

"Codex CLI not found"

1. Verify Codex is installed: codex --version
2. Check it's in your PATH: where codex (Windows) / which codex (Linux)
3. Restart Unreal Editor after installation

"Authentication required"

Run codex login in a terminal to authenticate.

Responses are slow

Codex executes in your project directory and may read files for context. Large projects may have slower initial responses.

You might also have too many global agent plugins enabled (i.e. Superpowers, ralp-loop, context7). The context for those plugins getting injected can cause slowdowns up to 3+ minutes.

Plugin doesn't compile

Ensure you're on Unreal Engine 5.7. Supported platforms are Windows (Win64), Linux, and macOS.

MCP Server not starting

Check if port 3000 is available. The MCP server logs to LogUnrealCodex.

MCP tools not available / Blueprint tools not working

If Codex reports that MCP tools are configured but unavailable:

1. Install MCP bridge dependencies: The most common cause is missing npm packages:

   cd YourProject/Plugins/UnrealCodex/Resources/mcp-bridge
   npm install

2. Verify the HTTP server is running: With the editor open, test:

   curl http://localhost:3000/mcp/status

   You should see a JSON response with project info.

3. Check the Output Log: Look for LogUnrealCodex messages:

   • MCP Server started on http://localhost:3000 - Server is running
   • Registered X MCP tools - Tools are loaded

4. Restart the editor: After installing npm dependencies, restart Unreal Editor.

Debugging the MCP Bridge

The MCP bridge is also available as a standalone repository with its own Vitest test suite. If you're experiencing bridge-level issues (tool listing, parameter translation, context injection), you can run the bridge tests independently:

cd path/to/ue5-mcp-bridge
npm install
npm test

This tests the bridge without requiring a running Unreal Editor.

Contributing

Feel free to fork for your own needs! Possible areas for improvement:

• Linux support (thanks @bearyjd)
• Mac support (thanks @lateralsummer)
• Additional MCP tools (the current toolset still needs refactoring, so no new tools for now)

License

MIT License - See LICENSE file.

Credits

• Built for Unreal Engine 5.7
• Integrates with OpenAI Codex CLI