Two independent Claude sessions. One problem. No shared context.

Send the same question to both panes at once and watch them diverge. Then hand one's answer to the other and watch it react.

Two panes

α and β each keep their own model, system prompt and history.

Cross-send

Fire β's reply at α as a new user message, in one click.

Presets

Sceptic ⚔ Builder · Red ⚔ Blue team · Line ⚔ Dev editor.

Web, files

Optional web search and fetch; drop in images, PDFs and code.

Try it like this

α: a sceptical architect — find the failure mode.
β: a pragmatic builder — find the path forward.
Send your design. Cross-send β's proposal to α.

What it needs from you

One Anthropic API key

—Requests go straight from this page to api.anthropic.com. There is no server in between and no account to make.

—Usage is billed to your own account. A running cost sits in the header from your first reply.

—Use a dedicated key with a spend limit. You can forget it from the header at any time.

API key

Keep it

Held in memory for this tab only. Closing it forgets the key.

Get a key ↗ console.anthropic.com/settings/keys

Designed and built by FoxxeLabs · MIT — fork of todd427/duel you bring the key; nobody else sees it

Settings

API key

Keep it

Requests go from this page straight to api.anthropic.com. Nothing is proxied and nothing is logged.

Beirt is another client for the Messages API, so it can reach any MCP server you can. Connections you configured elsewhere cannot be imported — no API gives them out — but these are remembered between sessions, and export as JSON if you want them on another machine.

Add a server

A new server starts disabled with an empty allow-list — it can reach nothing until you name the tools. Tokens follow the same session-or-remember choice as your API key.

Beirt /bʲɛrˠtʲ/ — “bert”, the final t softened toward tch
Irish for a pair of people. Two independent Claude sessions, side by side, with no shared context.

An open, bring-your-own-key fork of todd427/duel. The original routes through a hosted proxy that holds the key; this one has no server at all — you supply the key and it stays in your browser.

Designed and built by FoxxeLabs. MIT licensed. No analytics, no logging, no build step.

Themes: Paper and Folio are the house pair, Slate and Ink are neutral, Terminal comes from rialú.