Yab, Yet Another Browser README

yab-mcp

The MCP server of Yab, Yet Another Browser, for Claude Code, Codex, Cursor and any MCP client.

Yab, Yet Another Browser, is a free WebKit browser for the Mac. With this server, any agent gets one real browser on your Mac: the one you're signed in to. Your agent opens tabs of its own beside yours, reads pages as text, clicks, types and fills forms with your sign-ins, your cookies and your IP. There is no cloud browser, no debug port and no Chrome to set up, and it's free. A press on Send, Pay, Delete and the like waits for your yes on a card in Yab, unless you chose Bypass in Yab's settings: the browser holds that yes, not the model. Saved passwords are filled by Yab and never shown to the agent. Agent tabs live in a window off screen and come in front of you only when you ask. With Yab closed, the first call opens it hidden, with no window and no Dock tile, and it quits after half an hour with nothing to do. yab serve keeps it running that way.

Download Yab · For developers · Manual

Remote assistants (0.2.0 preview)

On the assistant's own computer, run npx yab-mcp login --client dots --nonce NONCE. It prints the code and returns immediately; a background process saves the connection after the person allows it in Yab. Yab on the Mac shows the eight-character code under Settings > AI > Assistants. After the person allows it there, use npx yab-mcp --remote as a stdio MCP server, or npx yab-mcp task "Find a table for Friday" to give Yab one task. The task command prints its session ID and returns; a shell-only assistant can run npx yab-mcp status SESSION to wait for the next update, or omit SESSION to check its newest task after a Mac reconnects. Repeat until it says done. The connection token stays in ~/.config/yab-mcp/auth.json (mode 0600), or the path in YAB_MCP_AUTH_FILE. YAB_MCP_URL selects a test server; production uses https://yab-sync.21st.workers.dev. Without --remote, this package still uses the local Yab app exactly as before.

Requirements

A Mac with macOS 15.4 or later.
Yab, free: download. It updates itself.
Agents allowed in Yab: Settings › AI › Agents › Let agents use Yab. Until then, every call says so.
Node.js 18 or later, for npx. A client can also run Yab directly, without Node: see Without Node.

Chrome is your main browser? Yab can still be the one your agents use, usually closed. yab import chrome brings Chrome's sign-ins into Yab after you say yes in Yab, so your agent hits fewer sign-in pages.

Already use Yab? Settings › Developers adds it to Claude Code and Codex with one click, and Copy Config gives the JSON for any other client. You don't need this package for that.

Install

Claude Code

The plugin brings the tools and Yab's skill:

Code

/plugin marketplace add yetanotherbrowser/yab-mcp
/plugin install yab@yab-mcp

From a shell: claude plugin marketplace add yetanotherbrowser/yab-mcp, then claude plugin install yab@yab-mcp.

Only the tools:

Terminal

claude mcp add --scope user yab-browser -- npx -y yab-mcp

If Yab's Settings › Developers already added Yab to Claude Code, skip this: you'd have the same tools twice.

Codex

The plugin, tools and skill:

codex plugin marketplace add yetanotherbrowser/yab-mcp
codex plugin add yab@yab-mcp

Or only the tools, in ~/.codex/config.toml:

toml

[mcp_servers.yab-browser]
command = "npx"
args = ["-y", "yab-mcp"]
tool_timeout_sec = 900
default_tools_approval_mode = "approve"

tool_timeout_sec lets a call wait up to 15 minutes while Yab asks you something; the plugin keeps Codex's default of 5. default_tools_approval_mode stops Codex asking before every Yab tool; Yab still asks you before Send, Pay and Delete. Leave it out if you want Codex to ask too.

Cursor

Or add it to ~/.cursor/mcp.json:

config.json

{
  "mcpServers": {
    "yab-browser": {
      "command": "npx",
      "args": ["-y", "yab-mcp"]
    }
  }
}

VS Code

code --add-mcp '{"name":"yab-browser","command":"npx","args":["-y","yab-mcp"]}'

Or in .vscode/mcp.json:

config.json

{
  "servers": {
    "yab-browser": {
      "type": "stdio",
      "command": "npx",
      "args": ["-y", "yab-mcp"]
    }
  }
}

Windsurf (Devin Desktop)

In ~/.config/devin/mcp_config.json (older Windsurf builds: ~/.codeium/windsurf/mcp_config.json):

config.json

{
  "mcpServers": {
    "yab-browser": {
      "command": "npx",
      "args": ["-y", "yab-mcp"]
    }
  }
}

Claude Desktop

Download yab-mcp-<version>.mcpb from Releases and open it: Claude Desktop installs it as an extension. Or add this to ~/Library/Application Support/Claude/claude_desktop_config.json:

config.json

{
  "mcpServers": {
    "yab-browser": {
      "command": "npx",
      "args": ["-y", "yab-mcp"]
    }
  }
}

Any other client

The same mcpServers entry: command npx, arguments -y yab-mcp, over stdio.

Without Node

Point the client at the app itself. This is what Yab's Copy Config gives:

config.json

{
  "mcpServers": {
    "yab-browser": {
      "command": "/Applications/yab.app/Contents/MacOS/yab",
      "args": ["mcp"],
      "env": { "YAB_CLI": "1" }
    }
  }
}

What yab-mcp does

It finds Yab: YAB_APP if set, then the app the yab command runs (~/.local/bin/yab), then yab.app in /Applications and ~/Applications, then Spotlight (mdfind, bundle id dev.serafim.fast).
It runs yab.app/Contents/MacOS/yab mcp with YAB_CLI=1. Your client talks to Yab directly: stdin and stdout go straight through, signals are passed on, and the exit code comes back.
Without Yab, or off a Mac, it serves a short built-in server instead. It lists Yab's tools from a snapshot and answers every call with how to get Yab.

It has no dependencies and makes no network requests of its own. npx yab-mcp --help says where it found Yab.

Tools

These come from a real tools/list of Yab, made by scripts/snapshot.mjs. The app you run is the final word: newer versions may list more.

Yab 0.0.18 lists 69 tools. Some appear only when you turn on what they need, as noted.

Tool	What it does
`devtools_comments`	Read user-authored comments on elements of an already inspected, non-private tab.
`devtools_console`	Read recorded Console messages from an already inspected, non-private tab.
`devtools_network`	Read sanitized request metadata recorded by the tab's Developer Tools.
`devtools_trace`	Read the WebKit Performance recording's event names, durations and nesting.
`devtools_styles`	Read the currently selected element's matched and computed styles from Developer Tools.
`native_context`	Read Yab's own current settings, spaces, tabs, mail accounts, permissions and this task's native operations.
`native_actions`	List native Yab actions with their strict argument schemas, targetKind, undo support and permission requirements.
`native_apply`	Perform a native Yab action explicitly requested by the user: settings, spaces, tabs, page fonts or connecting Gmail.
`native_operation`	Read this task's native operation by operationId, or wait for a change up to seconds (0 to 10).
`native_undo`	Undo a native change of this task by its changeId (or the last undoable change).
`tabs`	List the tabs open in Yab, the user's web browser: the user's and the agents'.
`open`	Open a web page (URL) in a new agent tab in Yab, the user's browser, signed in to their sites, beside the user's tabs.
`spaces`	List the user's spaces: sets of tabs, some signed in as someone else, with cookies of their own.
`navigate`	Send an agent tab to a URL, or back, forward or reload.
`snapshot`	Read a web page in a browser tab as an accessibility tree with ref ids.
`click`	Click an element by ref, as a real mouse click.
`type`	Replace the text in a field by ref (inputs, text areas, editors), or without ref, type into whatever has focus.

What leaves your Mac

This package: nothing. It reads a few files and asks Spotlight to find Yab, then starts it. npx downloads the package from the npm registry.
Between your agent and Yab: nothing leaves the Mac. yab mcp talks to the browser over a socket in Yab's folder that only your macOS user can open.
To your agent's model: what your agent reads with these tools, pages and, if you allow it, mail and messages, goes to the provider of the model your agent uses (Anthropic, OpenAI or another), under your account, as with anything else you give it. The task tool asks Yab to run Claude Code or Codex with your own plan, so the same applies there.
Yab itself: it checks yetanotherbrowser.com for updates, counts active days with a random installation ID (Settings › About › Share daily activity turns it off), and sends crash reports only if you say yes. Sync is off until you turn it on, and then end to end encrypted. Yab has no account, and no server of ours sees your browsing. Mail comes from Google straight to your Mac.
Websites get what any browser sends them.

Privacy Policy

Yab's privacy policy is at yetanotherbrowser.com/privacy. In short:

Collection: yab-mcp collects nothing. Yab keeps your tabs, history, passwords and mail on your Mac.
Use and storage: what Yab keeps stays in your user folder and the macOS keychain. Sync, if you turn it on, stores only end to end encrypted records.
Sharing: nobody at Yab gets your pages or mail. What an agent reads goes to that agent's provider, as above.
Retention: data on your Mac stays until you delete it. Sync data stays until you delete it in Settings › Sync. Yab's own records of updates and daily activity keep no IP address; the web host's request logs last a day at most.
Contact: serafimcloud@gmail.com, or Send Feedback in Yab.

Troubleshooting

"Agents are off in Yab": turn on Settings › AI › Agents › Let agents use Yab.
"Yab isn't installed on this Mac": install Yab, open it once, then restart the MCP server (in Claude Code: /mcp).
"The Yab that's running is older": quit Yab and open it again, so the running app matches the one on disk.
Yab lives somewhere else: set YAB_APP=/path/to/yab.app in the server's environment.

Development

Terminal

npm test                 # node --test, no dependencies
npm run snapshot         # new src/tools.json and README tool list from the Yab on this Mac
npm run pack:mcpb        # dist/yab-mcp-<version>.mcpb for Claude Desktop
npm run links            # the Cursor and VS Code install links

npm run snapshot sends Yab only initialize and tools/list, never a tool call. Releases and directory listings: PUBLISHING.md.

License

MIT, see LICENSE. Yab itself is free and closed source; this repository is its open part for agents.