Codex + Thrixel

Build 3D games with Codex and Thrixel

Describe a game. Codex writes the gameplay and builds the scene. Thrixel generates the 3D assets. The Build World skill gives Codex the process to bring it all together, playtest, and improve the result.

Paste into Codex 
Install the build-world skill from https://github.com/thrixel/build-world and follow the setup instructions in that repo.
Setup and first game ↓
A game built with Build World. More about the skill →

How It Works

The Build World skill guides the project. The Thrixel MCP server gives Codex the tools to create and edit its assets.

You

  • Describe the game and art style
  • Choose an engine
  • Give feedback as it develops

Codex

  • Plans the project
  • Writes gameplay and controls
  • Places assets in the scene
  • Playtests and fixes issues

Thrixel

  • Generates models from text or images
  • Edits individual parts
  • Adds detail and textures
  • Exports assets for the engine

Generate 3D Game Assets with Codex

Thrixel connects an AI 3D model generator to Codex through MCP, with tools for creating, editing, and exporting models directly from the game-building workflow.

  • Generate while Codex codes

    Props, vehicles, and environment models can generate while Codex works on game logic. A shared art direction guides the assets, and every model is saved to the Thrixel workspace.

  • Edit specific parts

    Structured models have named parts. Codex can change a roof, wheel, or sail from a text instruction, then add detail and textures once the shape is ready.

  • Improve through playtesting

    Build World uses a gauntlet loop to inspect the game and revise it. Thrixel gives Codex a way to act on visual feedback by refining models, materials, and asset budgets.

Choose an Engine

Name the engine in the prompt. Build World follows the workflow for that engine.

  • Three.js

    Browser games with JavaScript and GLB assets. Finished web builds can be published to thrixel.world as a playable link.

    Build a Three.js kart racer through a desert canyon with ramps and boost pads.
    Build World for web games →

  • Unity

    C# gameplay, Unity scenes, and FBX models. Unity WebGL builds can also be published to thrixel.world.

    Build a Unity hovercraft game with ancient ruins and moving obstacles.
    Thrixel for Unity →

  • Roblox

    Luau scripts synced with Rojo and models imported into Studio. Playtesting and publishing happen through Roblox Studio.

    Build a Roblox obby through a floating city with airships and spinning windmills.
    Thrixel for Roblox →

  • Unreal Engine

    FBX assets, Blueprint gameplay, and level editing through Unreal MCP. The agent inspects the scene and tests interactions in Play-In-Editor.

    Build an Unreal exploration game in an overgrown observatory with puzzle doors.
    Thrixel for Unreal Engine →

Make Games with Codex and GPT-6 Astra

GPT-6 Astra is an OpenAI model available in Codex for complex work across code and tools. In a game project, Codex uses the selected model to plan mechanics, write scripts, and inspect results. Thrixel provides the 3D models and asset editing tools.

Select Astra in the model controls when available to the account, or launch Codex CLI with codex -m gpt-6-astra. The official model guide covers availability and selection. Build World supplies the engine workflow whichever supported coding model is selected.

Get Started in Codex

This workflow runs in Codex on a computer with the chosen engine's tools. Start with Codex installed with access to the local project, and a Thrixel account for generating assets. For a walkthrough, read how to make a 3D game with Codex.

1 Ask Codex to install Build World.

Install the build-world skill from https://github.com/thrixel/build-world and follow the setup instructions in that repo.

Install both the Build World skill and the Thrixel MCP connection through the Codex setup flow. Follow the sign-in flow to connect a Thrixel account.

The Codex installation guide has the current plugin and manual setup options. Confirm that the Build World skill and Thrixel tools are available before starting the game.

2 Start a new Codex session and describe the game.

In Codex 
Use the Build World skill to build a submarine exploration game in Three.js set in a bright tropical sea, with coral reefs, sunken ruins, and treasure to collect

3 Refine the game with a follow-up prompt.

Example follow-up 
Add a lighthouse above the reef and a dock where the submarine can recharge. Playtest the route and check the camera near the dock.

For a finished Three.js or Unity WebGL game, ask Codex to publish it to thrixel.world and return a shareable link. Codex can publish updated builds after further changes.

Common Questions

How do Build World and MCP fit together?

Build World provides the game-building instructions: planning, engine setup, testing, and iteration. MCP connects Codex to Thrixel's asset tools. The Codex setup guide covers both pieces. The MCP server can also be used on its own for asset work.

Can Codex work on an existing game?

Codex can use Thrixel to generate missing props or replace placeholder models in an existing project. Generated assets stay in the Thrixel workspace, where they can be inspected, edited, and reused across games.

What accounts and tools are needed?

Codex access, a Thrixel account with generation credits, and the tools for the chosen engine. Unity uses the Unity Editor and Unity CLI; Roblox uses Studio and its setup workflow. Unreal uses the editor and Unreal MCP. Thrixel usage is separate from Codex usage. See the setup guide for details.