Crossbar

One chat for your coding agents. Crossbar is a VS Code sidebar that talks to the Codex and Claude Code runtimes already installed on your machine, keeps a single conversation history that survives switching between them, and shows what each provider actually reported rather than a guess.

What it does

• One conversation across both providers. Switching provider mid-thread carries the history forward instead of starting over.
• Compare a prompt across both providers side by side, then keep the answer you prefer as the one that continues the thread.
• Context Capsules: summarise a long thread into a structured attachment and continue from it when a session gets close to its context limit.
• Attach workspace files or selections, or drop text files from your file manager.
• Per-model reasoning effort. Each model advertises its own levels, and the composer offers only those, defaulting to the model's own setting.
• The selected model names itself. "Default (recommended)" shows the provider's own description underneath, so you always know what will actually run.
• Enter sends, Shift + Enter starts a new line.
• Tool calls, command output and diffs are shown as the runtime reports them, with approvals prompted in VS Code before anything runs.
• Usage and quota come from the provider itself. Nothing is estimated. When a limit is spent, the composer says so and when it lifts, instead of failing on your next send.
• Your local Claude Code configuration applies by default, so your skills, CLAUDE.md, hooks and MCP servers work as they do in the terminal.

Requirements

• VS Code 1.136 or newer, desktop. Crossbar lives in the secondary sidebar, alongside Claude Code and Codex, which needs that version.
• Node.js 20.19 or newer to build.
• A trusted, local, single-folder workspace. Crossbar stays inert in an untrusted or virtual workspace.
• At least one runtime installed and signed in:
  • Codex CLI, signed in with your ChatGPT account.
  • Claude Code, signed in with your Claude subscription.

Install

npm install
npm run package

That produces crossbar-0.1.0.vsix. Install it with code --install-extension crossbar-0.1.0.vsix, or from the Extensions view via "Install from VSIX".

Connecting providers

Open the secondary sidebar (View: Toggle Secondary Side Bar), pick the Crossbar tab, then Provider settings.

• Codex connects through the Codex CLI's own ChatGPT login. If Crossbar reports Codex as missing, the CLI is not on PATH. Set crossbar.codexPath to the executable. The Codex CLI bundled inside the ChatGPT VS Code extension works, for example ~/.vscode/extensions/openai.chatgpt-<version>/bin/macos-aarch64/codex.
• Claude connects through the Claude Code executable and the Agent SDK, using the subscription login already on the machine. Set crossbar.claudePath to choose an executable explicitly. By default Crossbar uses the runtime bundled with the official Claude Code extension, falling back to claude on PATH. The bundled runtime supports numeric subscription usage; older CLIs may not.

Settings:

Claude configuration modes

crossbar.claudeConfiguration decides how much of your machine's Claude Code setup a session loads. Verified command counts in a directory with a large skill library installed: full and skills both see 144, isolated sees 15.

Hooks run shell commands without a Crossbar approval prompt, since they are your own configuration. Choose skills if you want your skills without that.

Limitations

These are deliberate, not pending work.

• Subscription only. Crossbar never accepts an API key and never falls back to API billing. It drives the official local runtimes and uses whatever authentication they already hold. When you reach a plan limit, generation stops and Crossbar shows the runtime's own message, including when it resets. Keep paid extra usage disabled in your provider account if you want a hard ceiling.
• Shared limits. Usage through Crossbar draws on the same plan limits as using the runtimes directly. It does not add capacity.
• Desktop and local only. No remote, virtual, or untrusted workspaces, and a single workspace folder per window.
• No telemetry, no network of its own. Crossbar makes no network calls; only the provider runtimes do.
• Not published. The package identifier is crossbar with a local publisher. No Marketplace name is claimed or reserved.
• Effort levels are the provider's, not ours. Crossbar lists exactly what each model reports and sends nothing when you leave it on default. The sets differ per model, so a level chosen for one model is dropped rather than forced onto another that does not offer it. Models with no levels show no control.
• Usage refreshes automatically. Opening Usage requests current information, then refreshes every minute while visible and after responses. Claude and Codex show remaining percentages and reset times for their 5-hour and weekly windows when the runtime supplies them. Missing percentages are labelled unavailable; failed refreshes retain the last reading, which is marked stale after five minutes. Claude uses the pinned SDK's experimental structured usage request without submitting a model prompt; older runtimes may provide only limit status.

To attach context, drop text files onto the composer from VS Code Explorer or from your file manager. Explorer paths must stay inside the workspace. File-manager uploads attach the bytes you explicitly drop. Each file is limited to 150 KB; attachments together are limited to 20 items and 400,000 characters. Binary files are not supported. To attach an excerpt, select it in the editor, right-click, and choose Add to Crossbar chat. Review or remove attachments before sending.

Data

Conversations are stored as JSON under the extension's global storage directory, written atomically per conversation. Secrets matching common token shapes are redacted from logs and stored output. Nothing leaves the machine except the prompts the provider runtimes send on your behalf.

Development

npm run typecheck      # TypeScript, no emit
npm run lint           # ESLint
npm test               # Vitest, fake runtimes only
npm run build          # esbuild extension + webview
npm run test:webview   # Renders the webview in Chromium, dark and light, with axe
npm run test:vscode    # Launches VS Code in a throwaway profile and drives the view
npm run check:runtimes # Live check against your real accounts

check:runtimes and test:vscode accept CROSSBAR_CODEX_PATH and CROSSBAR_CLAUDE_PATH when the runtimes are not on PATH. Add --turn to check:runtimes to send one small real prompt to each connected provider; that consumes plan usage.

The unit tests never touch a real account. They drive the providers through fake processes and fake SDK streams.

License

MIT. See LICENSE. The bundled Claude Agent SDK keeps its own license, included in the build output as CLAUDE-SDK-LICENSE.md.