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| sidebar_position | title |
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| 6 | T3 Code |
T3 Code
T3 Code is a web-based coding agent harness from Theo Browne / ping.gg. Unlike the other harnesses listed here, T3 Code is not a CLI you talk to in a terminal — it runs a local web UI on port 3773 and orchestrates an underlying provider (Claude Code, Codex, or OpenCode) as the actual coding agent. You bring your own already-authenticated provider and T3 Code drives it from a browser.
Purpose
Use T3 Code when you want a browser UI over the same providers the other harnesses run from the terminal — multi-thread sessions, conversational history, and a UI for review/approval flows, while reusing whatever provider auth you already have set up in the sandbox.
Install
T3 Code is not preinstalled in the sandbox image. Run it on demand via npx:
npx t3
The first launch downloads the package and starts the server. No global install is required, but you can install it for faster subsequent starts:
pnpm add -g t3
Verify:
npx t3 --version
Authentication
T3 Code currently supports Codex, Claude, and OpenCode as backends. Install and authenticate at least one provider in the sandbox before launching T3 Code (see the per-provider pages for details):
- Codex: run
codex login - Claude Code: run
claudeand complete OAuth - OpenCode: run
opencode auth login
T3 Code itself uses a pairing-URL auth model: on first start it logs a one-time URL like http://localhost:3773/pair#token=... to stdout. Open that URL in your browser to bind the UI to the running server. The token is single-use; restart T3 Code to mint a fresh one.
Run in tmux
Per context/rules/sandbox-processes.md, long-running processes inside the sandbox go in named tmux sessions. T3 Code listens on 0.0.0.0:3773 so it can be reached from the host:
tmux new-session -d -s agent-t3code 'npx t3 2>&1 | tee /tmp/agent-t3code.log'
tmux capture-pane -t agent-t3code -p | grep -i pairingUrl
Open the printed pairing URL in your host browser. Reattach to the session at any time:
tmux attach -t agent-t3code
If you can't reach localhost:3773 from the host, expose port 3773 from the sandbox container (compose overlay or docker run -p 3773:3773), or front it with a Cloudflare tunnel — see Cloudflare integration.
Tips
- T3 Code is a UI over the providers — installing T3 Code does not replace
claude login/codex login/opencode auth login. Authenticate the provider first, then start T3 Code. - The pairing token is regenerated on every server restart. Treat it as ephemeral — don't bookmark the URL.
- T3 Code uses Node's experimental SQLite at startup; the warning in the log is expected.