trailofbits/chrome-mcp-troubleshooting

Claude in Chrome MCP Troubleshooting

Use this skill when Claude in Chrome MCP tools fail to connect or work unreliably.

When to Use

• mcp__claude-in-chrome__* tools fail with "Browser extension is not connected"
• Browser automation works erratically or times out
• After updating Claude Code or Claude.app
• When switching between Claude Code CLI and Claude.app (Cowork)
• Native host process is running but MCP tools still fail

When NOT to Use

• Linux or Windows users - This skill covers macOS-specific paths and tools (~/Library/Application Support/, osascript)
• General Chrome automation issues unrelated to the Claude extension
• Claude.app desktop issues (not browser-related)
• Network connectivity problems
• Chrome extension installation issues (use Chrome Web Store support)

The Claude.app vs Claude Code Conflict (Primary Issue)

Background: 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 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 extension requests a native host by name

3. If the wrong config is active, the wrong binary runs

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

5. Result: "Browser extension is not connected" even though everything appears to be running

The Fix: Disable Claude.app's Native Host

If you use Claude Code CLI for browser automation (not Cowork):

# 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

# Ensure the Claude Code config exists and points to the wrapper
cat ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json

If you use Cowork (Claude.app) for browser automation:

# 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

You cannot use both simultaneously. Pick one and disable the other.

Toggle Script

Add this to ~/.zshrc or run directly:

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?
# For Claude Code (single file in TMPDIR):
ls -la "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER" 2>&1

# For Claude.app (directory with PID files):
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

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.

Full Reset Procedure (Claude Code CLI)

# 1. Ensure correct config is active
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 the wrapper to use latest Claude Code version
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. Kill existing native host and clean sockets
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 for Chrome, click Claude extension icon

# 6. Verify correct native host is running
ps aux | grep chrome-native-host | grep -v grep
# Should show: ~/.local/share/claude/versions/X.X.X --chrome-native-host

# 7. Verify socket exists
ls -la "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER"

# 8. Restart Claude Code

Other Common Causes

Multiple Chrome Profiles

If you have the Claude extension installed in multiple Chrome profiles, each spawns its own native host and socket. This can cause 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)}"

Diagnostic Deep Dive

echo "=== Native Host Binary ==="
ps aux | grep chrome-native-host | grep -v grep

echo -e "\n=== Socket (Claude Code location) ==="
ls -la "$(getconf DARWIN_USER_TEMP_DIR)/claude-mcp-browser-bridge-$USER" 2>&1

echo -e "\n=== Socket (Claude.app location) ==="
ls -la /tmp/claude-mcp-browser-bridge-$USER/ 2>&1

echo -e "\n=== Native Host Open Files ==="
pgrep -f chrome-native-host | xargs -I {} lsof -p {} 2>/dev/null | grep -E "(sock|claude-mcp)"

echo -e "\n=== Active Native Messaging Configs ==="
ls ~/Library/Application\ Support/Google/Chrome/NativeMessagingHosts/com.anthropic*.json 2>/dev/null

echo -e "\n=== Custom Wrapper Contents ==="
cat ~/.claude/chrome/chrome-native-host 2>/dev/null || echo "No custom wrapper"

echo -e "\n=== TMPDIR ==="
echo "TMPDIR=$TMPDIR"
echo "Expected: $(getconf DARWIN_USER_TEMP_DIR)"

File Reference

File	Purpose
~/.claude/chrome/chrome-native-host	Custom wrapper script for Claude Code
/Applications/Claude.app/Contents/Helpers/chrome-native-host	Claude.app (Cowork) native host
~/.local/share/claude/versions/<version>	Claude Code binary (run with --chrome-native-host)
~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_browser_extension.json	Config for Claude.app native host
~/Library/Application Support/Google/Chrome/NativeMessagingHosts/com.anthropic.claude_code_browser_extension.json	Config for Claude Code native host
$TMPDIR/claude-mcp-browser-bridge-$USER	Socket file (Claude Code)
/tmp/claude-mcp-browser-bridge-$USER/<PID>.sock	Socket files (Claude.app)

Summary

1. Primary issue: Claude.app (Cowork) and Claude Code use different native hosts with incompatible socket formats
2. Fix: Disable the native messaging config for whichever one you're NOT using
3. After any fix: Must restart Chrome AND Claude Code (MCP connects at startup)
4. One profile: Only have Claude extension in one Chrome profile
5. One session: Only run one Claude Code instance

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Original skill by @jeffzwang from @ExaAILabs. Enhanced and updated for current versions of Claude Desktop and Claude Code.