Kitsune

Kitsune

Bring your coding agent into Firefox and keep working alongside it.

Kitsune lets AI agents such as Claude Code, Codex, Pi, and OpenCode use the Firefox, Zen, or LibreWolf browser you already have open. Your sessions, cookies, and extensions stay where they are, and there is no Playwright, Chromium, or WebDriver to install.

The agent can research in background tabs and prepare form drafts while you keep using the same browser. You stay with the agent you already use; Kitsune is not a separate browser or a built-in assistant.

The design follows two principles: the user's browser belongs to the user, and the agent gets fewer, sharper tools. See Philosophy.

A real run in Zen Browser. Page images are Kitsune's own screenshots of background tabs; the user's tab titles are hidden.

Why Kitsune?

• Tabs the agent creates open in the background. Kitsune holds writes to a tab you are actively using, and closing one of your own tabs takes a separate confirmation step. This reduces interference, but OS-level clicks and popups opened by sites still have focus and input limitations.
• You decide how much to delegate. KITSUNE_MODE=read, draft, or act limits both the tools the agent sees and the requests the bridge accepts. Draft mode lets the agent fill supported fields without click or submit tools, although sites may still autosave what it types. The default, act, has no such restriction. See Task modes.
• The agent starts with Playwright MCP's 25 core tools. Kitsune's other tools stay off until you allow them, and the agent can find and call the allowed ones without restarting its session. See Choosing tools.
• With the optional automation capability, an interrupted batch, parallel, or workflow call can be resumed without resending the writes that already succeeded. A write with an uncertain outcome needs an observation before it is retried. Checkpoints are temporary and are lost when the bridge restarts.

What can it do?

In your browser, the agent can:

• Search the web, read pages, and summarize what it finds with links.
• Click, type, select options, and fill forms, including on sites where you are already signed in.
• Take screenshots or turn page content into text and Markdown.
• Keep research and tasks in separate tabs without replacing the page you are using.

Benchmark

With the same tasks and tool allowlist, Kitsune v0.4.0 kept the user's tab in front in 23 of 24 shared-browser tasks, against 2 of 24 for Playwright MCP. On the tasks both solved, Kitsune cost 0.83 to 0.93 times as much. It solved 191 of 198 tasks, and Playwright MCP solved 197. Each task was run once with Claude Opus 5.5. Playwright MCP was not designed to share a browser with a person. See the full reports.

How is it different?

Kitsune is one of several ways to connect an agent to a browser. Which one fits depends on the browser you use and the work you want to hand off:

Kitsune connects through an extension and a local bridge, so Firefox needs no startup flags or WebDriver. Other Firefox extension projects also reuse your logins. Kitsune concentrates on sharing the browser with you while the agent works. Positioning has the full comparison and its limits.

How do I use it?

1. Install uv, then follow the MCP setup for your agent below. Install the browser extension in Firefox, Zen, or LibreWolf. The signed build stays installed; the developer build, which browser_evaluate needs, is a temporary add-on.
2. Keep the browser open. Kitsune starts its shared bridge automatically. Before your first task, ask the agent to check the connection.

3. Ask in plain language. For example:

   Research these three products in new background tabs and compare them with source links. Leave my current tab alone.

   Inspect this page's form and fill a draft. Don't submit it yet.

   Open Hacker News in a background tab and summarize the top three stories with links.

   Asking in plain language does not change the mode. To enforce a draft-only tool set, set KITSUNE_MODE=draft before starting the MCP client.

Use a dedicated browser profile, and give the agent access only to the accounts it needs. Have it ask you before it sends, buys, or deletes anything. The opt-in ask-before-act policy makes the bridge hold submits, payment pages, JavaScript, and cookie access until the agent repeats the call with a confirmation token. The agent can make that second call on its own, so it does not prove that a person approved, and none of these controls prevent prompt injection. Read the security guidance before using sensitive accounts.

MCP setup

Every client launches the same local stdio server: uvx --from kitsune-browser-mcp kitsune. Use only one setup method per client. Several clients can share one bridge; keep them on the same Kitsune version and install source.

CLI registration: Claude Code, Codex, and Pi

Claude Code, available in every project with --scope user:

claude mcp add --scope user kitsune -- uvx --from kitsune-browser-mcp kitsune

Codex CLI, which registers the server in ~/.codex/config.toml:

codex mcp add kitsune -- uvx --from kitsune-browser-mcp kitsune

Pi has built-in MCP support and registers servers for your user by default:

pi mcp add kitsune -- uvx --from kitsune-browser-mcp kitsune
pi mcp list

To register the server only for the current project, add --local before kitsune. In a Pi session that is already running, run /reload, then /mcp to check the connection. If an MCP adapter extension replaces Pi's built-in support, follow that extension's instructions instead.

OpenCode

Merge this into ~/.config/opencode/opencode.json (global) or opencode.json in your project root. OpenCode uses an mcp object with a command array, not mcpServers:

{
  "$schema": "https://opencode.ai/config.json",
  "mcp": {
    "kitsune": {
      "type": "local",
      "command": ["uvx", "--from", "kitsune-browser-mcp", "kitsune"],
      "enabled": true
    }
  }
}

JSON configuration: Pi, Claude Desktop, and Cursor

These clients use the same mcpServers format. Instead of CLI registration, where a client has it, you can merge this entry into the client's config file and keep any servers already there:

{
  "mcpServers": {
    "kitsune": {
      "command": "uvx",
      "args": ["--from", "kitsune-browser-mcp", "kitsune"]
    }
  }
}

After configuring a client, restart or reconnect it and ask it to list your tabs (browser_tabs with action: "list"). If that fails, the error's hint says what to fix. A GUI app that does not inherit your shell's PATH may need the full path from which uvx in place of uvx.

Choosing tools

By default Kitsune publishes Playwright MCP's 25 core tools with the same names, descriptions, and schemas, and they drive your own browser. Prompts and clients written for Playwright MCP work unchanged (Core tools). Kitsune's own tools are sorted into capability groups, which you enable with KITSUNE_CAPS in the MCP server's environment:

You can allow more tools than you publish, which keeps the agent's starting tool list small. With KITSUNE_CAPS=all and KITSUNE_PUBLISH=core, the agent starts with the core tools and can find and call the others in the same session (Finding tools without a restart). With Claude Code, for example:

claude mcp add --scope user kitsune -e KITSUNE_CAPS=all -e KITSUNE_PUBLISH=core -- uvx --from kitsune-browser-mcp kitsune

In the JSON configurations above, add "env": {"KITSUNE_CAPS": "all", "KITSUNE_PUBLISH": "core"} next to "args". The bridge checks the groups on every request, including batch steps. A tool called without a tab acts on the agent's current tab, not the one you are looking at.

If you are upgrading from 0.3: the devtools, parallel, windows and session groups were replaced by the groups above, and all no longer includes storage. A configuration that names a removed group fails at startup. Tools lists where each tool went.

Installation covers Codex's TOML configuration, environment variables, version pinning, and upgrades.

More documentation: Tools · Configuration · Troubleshooting · Updating · API reference · Development

The architecture, product trade-offs, and comparisons with other browser MCP servers are in Positioning.