Yab

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. When Yab's Connect flow supplies a nonce, add --nonce with that value. 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, choose who does the work:

• Direct browser control: configure your assistant's MCP server with command npx and args ["-y", "yab-mcp", "--remote"]. The assistant calls open, snapshot, click, type, etc. itself, using its own model/account. --remote bridges JSON-RPC over stdio; it does not accept a natural-language prompt or start a Yab model run. Calling the task MCP tool still delegates.
• Delegation: npx yab-mcp task "Find a table for Friday" starts a separate agent using the model selected for Tasks in Yab on the Mac. ChatGPT (via Codex) consumes the user's ChatGPT limits; Claude uses their Claude plan instead. Choose this when you intend to use that plan, including from a shell-only bot. It prints its session ID and returns; run npx yab-mcp status SESSION for the next update, or npx yab-mcp status for the newest task after a Mac reconnects. Repeat until it says done.

Both modes keep the assistant's existing account access and approval settings. The connection token stays in ~/.config/yab-mcp/auth.json (mode 0600), or the path in YAB_MCP_AUTH_FILE. When the home folder is read-only, as on some bots' computers, it goes to the first writable of /workspace/shared/.yab-mcp/, /workspace/.yab-mcp/ and .yab-mcp/ in the current folder. If the computer ends the background process that waits for the person's Allow, the next task, status or --remote finishes connecting. YAB_MCP_URL selects a test server; production uses https://yab-sync.21st.workers.dev. Plain npx yab-mcp starts the local app's MCP server.

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:

/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:

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:

[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

Add to Cursor

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

{
  "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):

{
  "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:

{
  "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:

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

What yab-mcp does

1. 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).
2. 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.
3. 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.
choose	Pick an option in a by its value or label.
press	Press keys on the focused element, as real key events.
hover	Rest the pointer on an element, as a mouse would: menus that open on hover open.
drag	Drag an element with the mouse: onto another element (to, its ref; the dragged one lands before it) or by dx, dy pixels.
dialog	Answer what the page asked with alert, confirm or prompt: accept (OK) or not (Cancel), and text for a prompt.
scroll	Scroll the page, or the box around an element by ref (lists marked scrolls), by dy pixels (negative is up).
run	Run JavaScript that drives tabs with the same tools, several steps in one call.
text	A tab's whole visible text, for reading articles and results.
screenshot	A picture of a tab as it is now, for when the snapshot is not enough.
wait	Wait for a tab to finish loading, or until its text contains for.
eval	Run JavaScript in an agent tab (isolated from the page's own scripts, same DOM) and return its value.
close	Close an agent tab.
show	Put a tab in front of the user as one of theirs.
memory_search	Search what you know about the user from earlier tasks, who they are, their accounts and sites, people, projects.
memory_read	Read one memory page whole: USER (who the user is), MEMORY (how to work for them), TAXONOMY.
profile	The user's profile for forms: name, headline, company, role, location, linkedin, x, github, website, telegram.
form_answers	Answers the user typed into web forms, kept with nothing asked once the form went through.
remember	Keep something for later tasks.
history	The user's browsing history.
watch	Watch a thread for someone's reply: every two hours for days.
suggest	Hand the user what needs them, as quiet rows under a new tab's field.
boosts	List saved site boosts, their sites, permissions and state.
boost_read	Read the files of a saved boost or this task's trial before changing it.
skills	Yab's skills: how particular sites work for an agent (Gmail, GitHub, LinkedIn, Amazon, …), a line each.
skill	Read one skill whole, by name.
handoff	Ask the user to take over a tab, sign in, pass a captcha, enter a code, and wait until they say they are done.
ask	Ask the user to pick: a question with up to four options (they may also write their own), shown at the foot of a tab.
sign_in	Sign in on this tab's page with a password Yab has saved for the site (the user may be asked first).
autofill	Fill a form on this tab with what Yab keeps for the user.
upload	Give the page files from this Mac (the user may be asked first).
download	Download a file: click ref (a download link or button), or fetch url with the tab's cookies.
pdf	Save a tab's page as a PDF in the task's folder; returns the path.
fetch	Read a URL with the user's cookies, no tab needed.
mail_triage	The user's mail as yab already sorted it on this Mac. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_search	Search all of the user's mail, of any age. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_read	A thread of the user's mail as text, oldest message first, with its labels by name, the files each message carries. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_file	The words of a file a thread of the user's mail carries. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_draft	Write a reply in a thread (thread), a forward of a thread's last mail (thread, forward: true, to), or a new mail. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_send	Send a mail that is in yab's mail page, only when the user asked for exactly that mail to go. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_act	Tidy a thread of the user's mail, as they would in yab's mail page. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_labels	The user's own labels in their Gmail, and the list itself. Listed with a Gmail account connected in Yab (Settings › Mail).
mail_recall	Search all of the user's mail of the last 5 years, kept on this Mac, by what it says as well as its words. Listed when agents may search all your mail (Settings › Mail).
mail_code	Read the one-time code the tab's own site mailed to the user in the last minutes (default 10), from their Gmail. Listed when Yab may read sign-in codes from Gmail (Settings › Autofill).
messages	The user's Messages (iMessage and texts): with no chat, their chats, most recent first, each with its last line. Listed when agents may use Messages (Settings › AI › Agents).
send_message	Send a message through Messages to a phone number or an address. Listed when agents may use Messages (Settings › AI › Agents).
messages_code	Read the latest one-time code from the user's Messages. Listed when agents may use Messages (Settings › AI › Agents).
name	Name this task: once it has more than one tab they sit in a folder in the user's tab list.
task	Hand a whole browser job to an agent Yab runs itself (Claude Code, or Codex), and wait for its answer.
task_status	What a task is doing now, and its answer when it is done.
task_stop	Stop a task.
task_steer	Redirect a running task now: it reads this at its next step.
task_queue	Give a task something to do after what it is doing now.

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: [email protected], 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

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.