Claude in Chrome Troubleshooting

Diagnose and fix Claude in Chrome MCP extension connectivity issues

Original Author: @jeffzwang from @ExaAILabs

Enhanced by: Trail of Bits

Overview

Diagnose and fix Claude in Chrome MCP extension connectivity issues. This plugin provides systematic troubleshooting for browser automation failures, focusing on the primary conflict between Claude.app (Cowork) and Claude Code native messaging hosts.

When to Use

Connection Failures

mcp__claude-in-chrome__* tools fail with “Browser extension is not connected”

Erratic Behavior

Browser automation works inconsistently or times out

After Updates

Problems appear after updating Claude Code or Claude.app

Switching Contexts

Issues when switching between Claude Code CLI and Claude.app (Cowork)

The Core Issue

When Claude.app added Cowork support (browser automation from the desktop app), it introduced a competing native messaging host that conflicts with Claude Code CLI.

Two Native Hosts, Two Socket Formats

Component	Native Host Binary	Socket Location
Claude.app (Cowork)	/Applications/Claude.app/Contents/Helpers/chrome-native-host	/tmp/claude-mcp-browser-bridge-$USER/<PID>.sock
Claude Code CLI	~/.local/share/claude/versions/<version> --chrome-native-host	$TMPDIR/claude-mcp-browser-bridge-$USER (single file)

Why They Conflict

1. Both Register Configs

   Both register native messaging configs in Chrome:

   • com.anthropic.claude_browser_extension.json → Claude.app helper
   • com.anthropic.claude_code_browser_extension.json → Claude Code wrapper
2. Chrome Requests Host

   Chrome extension requests a native host by name

3. Wrong Binary Runs

   If the wrong config is active, the wrong binary runs

4. Incompatible Sockets

   The wrong binary creates sockets in a format/location the MCP client doesn’t expect

5. Connection Fails

   Result: “Browser extension is not connected” even though everything appears to be running

Quick Fix

You cannot use both Claude.app (Cowork) and Claude Code CLI simultaneously. Pick one and disable the other.

For Claude Code CLI

# Disable the Claude.app native messaging config
mv ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_browser_extension.json \
   ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_browser_extension.json.disabled

# Verify Claude Code config exists
cat ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json

For Claude.app (Cowork)

# Disable the Claude Code native messaging config
mv ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json \
   ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json.disabled

Toggle Script

Add this to ~/.zshrc to easily switch between Claude.app and Claude Code:

chrome-mcp-toggle() {
    local CONFIG_DIR=~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts
    local CLAUDE_APP="$CONFIG_DIR/com.anthropic.claude_browser_extension.json"
    local CLAUDE_CODE="$CONFIG_DIR/com.anthropic.claude_code_browser_extension.json"

    if [[ -f "$CLAUDE_APP" && ! -f "$CLAUDE_APP.disabled" ]]; then
        # Currently using Claude.app, switch to Claude Code
        mv "$CLAUDE_APP" "$CLAUDE_APP.disabled"
        [[ -f "$CLAUDE_CODE.disabled" ]] && mv "$CLAUDE_CODE.disabled" "$CLAUDE_CODE"
        echo "Switched to Claude Code CLI"
        echo "Restart Chrome and Claude Code to apply"
    elif [[ -f "$CLAUDE_CODE" && ! -f "$CLAUDE_CODE.disabled" ]]; then
        # Currently using Claude Code, switch to Claude.app
        mv "$CLAUDE_CODE" "$CLAUDE_CODE.disabled"
        [[ -f "$CLAUDE_APP.disabled" ]] && mv "$CLAUDE_APP.disabled" "$CLAUDE_APP"
        echo "Switched to Claude.app (Cowork)"
        echo "Restart Chrome to apply"
    else
        echo "Current state unclear. Check configs:"
        ls -la "$CONFIG_DIR"/com.anthropic*.json* 2>/dev/null
    fi
}

Usage: chrome-mcp-toggle then restart Chrome (and Claude Code if switching to CLI).

Quick Diagnosis

# 1. Which native host binary is running?
ps aux | grep chrome-native-host | grep -v grep
# Claude.app: /Applications/Claude.app/Contents/Helpers/chrome-native-host
# Claude Code: ~/.local/share/claude/versions/X.X.X --chrome-native-host

# 2. Where is the socket? (Claude Code)
ls -la "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER" 2>&1

# 2. Where is the socket? (Claude.app)
ls -la /tmp/claude-mcp-browser-bridge-$USER/ 2>&1

# 3. What's the native host connected to?
lsof -U 2>&1 | grep claude-mcp-browser-bridge

# 4. Which configs are active?
ls ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic*.json

Full Reset Procedure

Critical Insight: MCP connects at startup. If the browser bridge wasn’t ready when Claude Code started, the connection will fail for the entire session. The fix is usually: ensure Chrome + extension are running with correct config, THEN restart Claude Code.

1. Ensure Correct Config

   mv ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_browser_extension.json \
      ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_browser_extension.json.disabled 2>/dev/null
   
2. Update Wrapper

   cat > ~/.claude/chrome/chrome-native-host << 'EOF'
   #!/bin/bash
   LATEST=$(ls -t ~/.local/share/claude/versions/ 2>/dev/null | head -1)
   exec "$HOME/.local/share/claude/versions/$LATEST" --chrome-native-host
   EOF
   chmod +x ~/.claude/chrome/chrome-native-host
   
3. Clean Up

   pkill -f chrome-native-host
   rm -rf /tmp/claude-mcp-browser-bridge-$USER/
   rm -f "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER"
   
4. Restart Chrome

   osascript -e 'quit app "Google Chrome"' && sleep 2 && open -a "Google Chrome"
   
5. Wait and Click Extension

   Wait for Chrome to fully load, then click the Claude extension icon

6. Verify Native Host

   ps aux | grep chrome-native-host | grep -v grep
   # Should show: ~/.local/share/claude/versions/X.X.X --chrome-native-host
   
7. Verify Socket

   ls -la "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER"
   
8. Restart Claude Code

   Now restart your Claude Code session

Other Common Issues

Multiple Chrome Profiles

If you have the Claude extension installed in multiple Chrome profiles, each spawns its own native host and socket, causing confusion.

Fix: Only enable the Claude extension in ONE Chrome profile.

Multiple Claude Code Sessions

Running multiple Claude Code instances can cause socket conflicts.

Fix: Only run one Claude Code session at a time, or use /mcp to reconnect after closing other sessions.

Hardcoded Version in Wrapper

The wrapper at ~/.claude/chrome/chrome-native-host may have a hardcoded version that becomes stale after updates.

Diagnosis:

cat ~/.claude/chrome/chrome-native-host
# Bad: exec "/Users/.../.local/share/claude/versions/2.0.76" --chrome-native-host
# Good: Uses $(ls -t ...) to find latest

Fix: Use the dynamic version wrapper shown in the Full Reset Procedure above.

TMPDIR Not Set

Claude Code expects TMPDIR to be set to find the socket.

# Check
echo $TMPDIR
# Should show: /var/folders/XX/.../T/

# Fix: Add to ~/.zshrc
export TMPDIR="${TMPDIR:-$(getconf DARWIN_USER_TEMP_DIR)}"

Installation

/plugin install trailofbits/skills/plugins/claude-in-chrome-troubleshooting

Platform Support

This plugin is macOS-specific and covers paths and tools like ~/Library/Application Support/ and osascript. It does not support Linux or Windows.

License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License.