arc-cdp-mcp

An MCP server that gives Claude Code control of Arc — navigate, click, fill forms, screenshot, read console and network traffic. It exists because the official "Claude in Chrome" extension does not work in Arc.

It talks to Arc over the Chrome DevTools Protocol, skipping the extension layer entirely.

Why the official extension fails in Arc

If you installed the Claude extension in Arc and nothing happens, here is what is actually going on. The extension is installed and its native-messaging channel to Claude Code does work — commands reach Arc. Two things break after that:

1. The side panel. The service worker checks for chrome.sidePanel and falls back to a notification whose text is right there in the bundle:

Claude requires the Chrome Side Panel API, which isn't available in this browser. Use Google Chrome, Microsoft Edge, or Brave.

Arc has the API schema compiled in, but its side panel is a custom implementation (ArcBrowserSidePanel) that is not exposed to extensions.

2. New tabs. Arc's new tab is chrome://start-page/<uuid>, which isn't navigable from an extension context — it fails with ERR_INVALID_URL. The tab-group handshake then hangs waiting for a page that will never be ready.

Since Claude Code runs in the terminal, the side panel isn't the part you need — the automation is. So this server drops the extension and speaks CDP to Arc directly.

Requirements

macOS, Arc, Node 18+, and Claude Code.

Install

git clone https://github.com/chmodami/arc-cdp-mcp
cd arc-cdp-mcp
npm install
claude mcp add arc-cdp --scope user -- node "$PWD/src/server.js"

Restart Claude Code — MCP servers load at session start.

Running

Arc has to be launched with a debugging port. It must be fully quit first; the flag only applies to a new process.

./arc-start.sh

The script quits Arc, relaunches it with --remote-debugging-port=9222, and waits for CDP to answer. Opening Arc from the Dock afterwards won't carry the flag.

For a different port: ./arc-start.sh 9333, and set ARC_CDP_URL=http://127.0.0.1:9333.

Tools

The intended loop is arc_read_page → take a ref → arc_click/arc_type, rather than guessing CSS selectors. Refs are reassigned on every read, so read again after anything that changes the DOM.

Your tabs vs. the server's tabs

CDP can see every Arc tab, including your bank and your email. To keep an implicit call from ever landing on one:

• Tabs this server opened are owned: true; tabs that already existed are owned: false.

• The active tab — used when tabId is omitted — is always an owned one.

• Targeting one of your tabs requires passing its tabId explicitly.

• arc_close_tab refuses to close a tab it doesn't own.

Be clear about what this is: a convention inside the server, not a sandbox. An explicit tabId still reaches any tab. CDP has no per-site permission model — the official extension's site-by-site approval is a real protection you give up here. Decide whether that trade is right for you before installing.

Teaching your agent to use it

The tools show up on their own, but Claude Code still sees the mcp__claude-in-chrome__* tools and may reach for those first — they connect, accept commands, and then time out. skill/arc-browser.md is a skill that tells the agent to use arc_* instead, along with the read-then-act loop and the tab rules. Install it with:

mkdir -p ~/.claude/skills/arc-browser
sed "s|<REPO_PATH>|$PWD|g" skill/arc-browser.md > ~/.claude/skills/arc-browser/SKILL.md

Limitations

• Arc must be launched with the flag. Without it, every tool returns an error telling you how to relaunch.

• Tabs Arc has suspended have no renderer and stay invisible until they load.

• No side panel: this is automation only, not Claude chat inside the browser.

• macOS only, because arc-start.sh uses open and osascript.

Prior art

arc-browser-mcp also drives Arc, with an AppleScript engine alongside CDP. Worth a look — it may fit you better.

License

MIT