Build Games with an AI Agent: Claude Code or Codex + Unity | AI Guides

How to go from zero to playable game prototypes with an AI coding agent driving Unity. You do not need Zo for any of this. You need a computer, a Claude or ChatGPT plan, and Unity. Tools in this space change monthly. Where a step here disagrees with the official page linked next to it, the official page wins.

Why try it

Making a game used to mean months of C# and editor know-how before anything was playable. An AI agent connected to Unity removes most of that wait. You describe the mechanic, the agent writes the scripts, wires up the scene, reads the error console, and fixes its own mistakes, while you make the design calls.

That makes it realistic to finish small games on evenings and weekends, whether you are learning, prototyping an idea, or just having fun with it.

What you need

An AI coding agent and a plan. Claude Code (needs Claude Pro or higher, see claude.com/pricing) or Codex (needs a ChatGPT plan with Codex, see chatgpt.com/pricing). The entry plan is enough to start. If you have never installed one, do the Claude Code and Codex: Setup for Beginners guide first. It takes about ten minutes.
Unity. Install Unity Hub from unity.com/download, then install a Unity 6 editor from inside the Hub. Unity has a free Personal plan. Unity 6 or later is required for Unity's official agent plugin.
A project. In Unity Hub, create a new project from a template (3D or 2D core is fine). Remember where it is saved. That folder is where you will start your agent.

The two pieces: skills and live editor control

There are two separate things you can give your agent, and it helps to know which is which.

Unity's official plugin (skills). A pack of Unity-written instructions that teach your agent how Unity actually wants things done: UI Toolkit, 2D and tilemaps, localization, multiplayer, in-app purchases, render pipeline features. It installs into Claude Code or Codex with two commands. It works on files and through the Unity command line.
Live editor control (MCP). A connection that lets the agent see and operate the running Unity Editor: read the scene hierarchy, create and edit GameObjects, change component values, and read the console. MCP stands for Model Context Protocol, the standard way agents plug into other programs. Learn more in Plugins, Skills, and MCP.

Start with the plugin. Add live editor control once you want the agent to work inside open scenes, not just in script files.

Step 1: Install Unity's plugin

Claude Code. Open a terminal in your Unity project folder, type claude, then run these two commands inside the session:

/plugin marketplace add Unity-Technologies/unity-agent-plugin

/plugin install unity@unity-agent-plugin

When it asks for a scope, pick user if you will work across several Unity projects. Type /unity: to see the Unity skills in the menu. Official instructions, including the Claude desktop app route: docs.unity.com: Unity's plugin for Claude Code.

Codex. In a terminal, run:

codex plugin marketplace add Unity-Technologies/unity-agent-plugin

codex plugin add unity@unity-agent-plugin

Start a new Codex session and type /unity: to confirm. Official instructions: docs.unity.com: Unity's plugin for Codex. The skill list lives in the unity-agent-plugin repository.

Step 2: Add live editor control (optional, recommended)

Pick one of two routes.

Route A: Unity's official MCP server. Built into Unity's AI Assistant package. Requirements per Unity: Unity 6 or later, the AI Assistant package, a project connected to Unity Cloud, and an active trial or subscription to Unity's AI tools. In the editor go to Edit > Project Settings > AI > Unity MCP, check the bridge shows Running, open Integrations, pick Claude Code or Codex, and press Configure. The first time your agent connects, Unity shows a pending connection that you must Accept. Walkthrough: Unity's MCP getting-started post.

Route B: MCP for Unity (free, open source). A community bridge, MIT licensed, that works on Unity 2021.3 LTS through 6.x with no Unity AI subscription. It installs through the Package Manager from a git URL and needs Python 3.10 or newer via uv. Follow the install steps in CoplayDev/unity-mcp. Good choice if you are on an older Unity version or do not want another subscription.

Test either route by asking: Read the Unity console and summarize any warnings or errors. If the agent answers from the live console, you are connected.

Step 3: Your first session

Start the agent in your Unity project folder. Good first prompts, one at a time:

Look at this Unity project and tell me what is in it, like I am new to Unity.
Create a simple first-person controller: WASD to move, mouse to look, space to jump. Put it in a new scene called Prototype01.
Add three platforms at different heights and a coin that disappears when I touch it. Keep a coin counter on screen.
Press play in your head: what will break first? Check the console and fix anything you find.

Then press Play in Unity and try it. Tell the agent exactly what felt wrong ("the jump is floaty", "the camera clips into walls"). That feedback loop is the job: you are the designer, the agent is a fast junior engineer.

A 30-day first game

The goal is several small finished things, not one big unfinished thing.

Week 1: one mechanic. Pick a single verb (jump, grapple, dash, stack, aim). Build three variations of it in separate scenes. Keep the one that feels best.
Week 2: make it a game. Add a goal, a fail state, a restart, and a score. Ten minutes of play is plenty.
Week 3: polish what a player sees first. Menu, sound, screen shake, a title. Ask the agent for "juice" ideas and pick the ones you like.
Week 4: ship it. Make a WebGL build and upload it to itch.io so anyone can play in a browser. Record a 30 to 60 second clip. Write a short post on what you were testing and what you changed after playtesting.

Then do it again with a different mechanic. A few small finished games teach you more than one big unfinished one.

Habits that keep it working

Save working versions. Ask the agent: Set up git for this Unity project with a proper Unity .gitignore and commit this as a working version. Commit every time something works.
One prototype per scene. Small scenes keep the agent's attention focused and make breakage easy to undo.
Name the system you want. Unity has several UI systems. Unity recommends saying "UI Toolkit" for new projects, or "uGUI" if the project already uses it.
Read before you approve. Watch for anything that deletes assets or touches folders outside your project.
Ask it to read the skill. If a Unity task comes back wrong, ask the agent to read the relevant skill's reference files and try again. This is one of Unity's own best-practice tips for the plugin.

Fixes for the common snags

The agent connects to Unity, then the connection drops or says "revoked". In Project Settings > AI > Unity MCP, toggle the connection off and on, then restart your agent session. Unity's forum tracks open issues for this.
The /plugin command does nothing. You are probably in the VS Code extension. Type /plugins there to open the plugin manager instead, or use the terminal.
The agent edits scripts but nothing changes in the scene. That is the difference between skills and live control. Add Step 2, or ask the agent to tell you which objects to drag where.
Unity shows compile errors after an agent change. Paste nothing. Ask: Read the Unity console and fix the compile errors. With live control connected it reads them itself.

Where to go next

Unity Learn for free lessons on the engine itself. Knowing what a prefab or a Rigidbody is makes your prompts much sharper.
Prompting and Persona Craft for getting better output from any agent.
Plugins, Skills, and MCP for connecting your agent to other tools (Blender, image tools, your own scripts).