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Get started with T3 Code

T3 Code is a minimal web GUI for coding agents like Codex. Get up and running in just a few steps.
1

Install Codex CLI

Before using T3 Code, you need to have the Codex CLI installed and authorized.
# Install Codex CLI
# Follow instructions at https://github.com/openai/codex
T3 Code requires Codex CLI to be available on your PATH and authenticated. The server starts codex app-server per session.
2

Launch T3 Code

Choose your preferred method to run T3 Code:
Run T3 Code instantly without installation:
npx t3
This will:
  • Start the Node.js WebSocket server
  • Serve the React web interface
  • Open your browser automatically
  • Connect to ws://localhost:3773
The NPX method is perfect for trying T3 Code or using it occasionally without a full installation.
3

Start your first session

Once T3 Code is running, you’ll see the web interface:
  1. Select a runtime mode:
    • Full access (default): No approval required, full system access (approvalPolicy: never, sandboxMode: danger-full-access)
    • Supervised: Prompts for command/file approvals (approvalPolicy: on-request, sandboxMode: workspace-write)
  2. Create or select a project: Organize your work with persistent projects
  3. Start coding: Type your request in the chat interface and let Codex help you code

Learn about runtime modes

Understand the security implications of each runtime mode
4

Verify everything works

Try a simple task to verify your setup:
Example prompt
Create a simple hello.js file that prints "Hello from T3 Code!"
You should see:
  • Codex processing your request
  • Real-time updates in the chat
  • File creation and modifications
  • Git checkpointing (if in a git repository)
If you see the file created successfully, you’re all set!

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What’s happening under the hood

When you run T3 Code, the following architecture is established: 
┌─────────────────────────────────┐
│  Browser (React + Vite)         │
│  Connected via WebSocket        │
└──────────┬──────────────────────┘
           │ ws://localhost:3773
┌──────────▼──────────────────────┐
│  apps/server (Node.js)          │
│  WebSocket + HTTP static server │
│  ProviderManager                │
│  CodexAppServerManager          │
└──────────┬──────────────────────┘
           │ JSON-RPC over stdio
┌──────────▼──────────────────────┐
│  codex app-server               │
└─────────────────────────────────┘
T3 Code wraps codex app-server (JSON-RPC over stdio) and streams structured events to the browser through WebSocket push messages.

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Next steps

Core Concepts

Understand sessions, providers, and the architecture

Project Management

Learn how to organize your work with projects and threads

Git Workflow

Discover how T3 Code handles version control and checkpointing

Configuration

Customize T3 Code for your workflow

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Troubleshooting

Ensure Codex CLI is installed and available on your PATH:
which codex
# Should output the path to codex binary
If not found, install Codex CLI from https://github.com/openai/codex
Authenticate Codex before running T3 Code:
# Use API key or ChatGPT auth supported by Codex
codex auth
Another instance of T3 Code might be running. Kill the existing process or use a different port:
# Find and kill the process
lsof -ti:3773 | xargs kill -9
Check that:
  • The server started successfully
  • No firewall is blocking localhost:3773
  • Your browser supports WebSockets
Refresh the page or restart T3 Code.
Need help? Join our Discord community or check out the GitHub repository.
T3 Code is in very early development. Expect bugs and breaking changes.

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