Claude in Chrome: extension never registers with MCP server — list_connected_browsers always returns [] despite correct install, permissions, account, and open side panel

Description

The claude-in-chrome MCP server is reachable from Claude Code, but no browser ever registers with it. mcp__claude-in-chrome__list_connected_browsers returns [] and tabs_context_mcp returns "Browser extension is not connected" on every call, across seven attempts and four rounds of remediation (including a full extension reinstall and multiple /mcp reconnects).

Every documented cause appears to be ruled out — see "Ruled out" below.

Environment

| | |
|---|---|
| Claude Code | 2.1.220 |
| Chrome | 150.0.7871.182 (stable, macOS) |
| Extension | Claude, v1.0.81, id fcoeoabgfenejglbffodgkkbkcdhcgfn |
| macOS | 15.5 (24F74), Apple Silicon |
| Chrome profile | Default (the only profile on this machine) |

Also installed but not in use for this: Arc, Brave, Chromium. Arc was running concurrently with Chrome.

Steps to reproduce

1. Install the Claude extension from the Web Store into Chrome.
2. Sign into claude.ai in Chrome with the same account used by Claude Code.
3. Open the extension side panel; confirm it loads and shows the correct account.
4. In Claude Code, call mcp__claude-in-chrome__list_connected_browsers.

Expected

The browser appears in list_connected_browsers, and tabs_context_mcp returns tab context.

Actual

mcp__claude-in-chrome__list_connected_browsers  →  []

mcp__claude-in-chrome__tabs_context_mcp  →
Browser extension is not connected. Please ensure the Claude browser extension
is installed and running (https://claude.ai/chrome), and that you are logged
into claude.ai with the same account as Claude Code. ...

Reproduced 7 times over ~30 minutes, interleaved with the remediation steps below. Result was identical every time.

Ruled out

Verified directly against the Chrome profile on disk, not just visually:

• Extension installed and enabled. Present in Default/Extensions/fcoeoabgfenejglbffodgkkbkcdhcgfn/1.0.81_0. In Secure Preferences: disable_reasons: [], from_webstore: true, location: 1.
• Host permissions granted. granted_permissions includes <all_urls>, https://claude.ai/*, https://*.claude.ai/*.
• Correct account. claude.ai signed in as the same account as Claude Code; confirmed in the side panel UI.
• Side panel opened. Panel loads and is fully functional as a standalone agent (model selector, "Ask before acting" permission control both render and work).
• Single profile. No chance of the extension living in a profile other than the active one.
• Not a wrong-browser mixup. Extension is in Google Chrome; verified Chrome (not Arc) was the browser signed in and running the panel.
• Clean reinstall performed. Extension removed and reinstalled; no change.
• MCP transport is healthy. /mcp reports "Reconnected to claude-in-chrome" and tool calls reach the server and return structured responses — the server is up, it simply has no registered browsers.

Notes

The side panel works perfectly as a standalone Chrome agent, which suggests the extension's own auth and connectivity to claude.ai are fine. What fails is specifically the registration that makes the browser visible to Claude Code's MCP server, so the break looks isolated to that pairing path rather than to extension auth generally.

No user-facing affordance was found for initiating the pairing manually — no visible "connect to Claude Code" control in the side panel or its overflow menu. If one exists, surfacing it (or surfacing why registration failed) would have made this self-diagnosable; as it stands the error message lists causes that were all already satisfied.