Skip to main content
Original Author: @jeffzwang from @ExaAILabsEnhanced 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

ComponentNative Host BinarySocket 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.
# 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

​
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

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.
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.
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.
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.

Build docs developers (and LLMs) love

Get started for freeTalk to us