chrome-devtools

# Chrome DevTools MCP Skill

Control Chrome browser programmatically via chrome-devtools-mcp.

**⚡ Performance Tip:** Always use the patterns in "Quick Start" section below. They include cleanup and run everything in ONE command to avoid browser lock issues.

**Speed Comparison:**
- ❌ **OLD WAY:** Multiple attempts, manual cleanup, 5-10 commands → ~60-90 seconds
- ✅ **NEW WAY:** One optimized command → ~5-10 seconds

**📚 See also:** MCP CLI patterns and best practices (see create-mcp-skill skill for reference)

## Setup

```bash
# macOS
brew tap f/mcptools
brew install mcp

# Windows/Linux
go install github.com/f/mcptools/cmd/mcptools@latest
```

## Quick Start (FASTEST)

### Check Console Errors on localhost

**Single command (copy-paste ready):**
```bash
pkill -9 -f "chrome-devtools-mcp" 2>/dev/null; sleep 1; echo -e 'navigate_page {"url":"http://localhost:3000"}\nlist_console_messages {"pageIdx":0}\nexit' | timeout 30 mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

### Full Debug: Console + Network + Page Content

```bash
pkill -9 -f "chrome-devtools-mcp" 2>/dev/null; sleep 1; echo -e 'navigate_page {"url":"http://localhost:3000"}\nlist_console_messages {"pageIdx":0}\nlist_network_requests {"pageIdx":0}\ntake_snapshot {"verbose":true}\nexit' | timeout 30 mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

### Screenshot a Page

```bash
pkill -9 -f "chrome-devtools-mcp" 2>/dev/null; sleep 1; echo -e 'navigate_page {"url":"https://example.com"}\ntake_screenshot {"fullPage":true,"format":"png"}\nexit' | timeout 30 mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

### Execute JavaScript on Page

```bash
pkill -9 -f "chrome-devtools-mcp" 2>/dev/null; sleep 1; echo -e 'navigate_page {"url":"http://localhost:3000"}\nevaluate_script {"function":"() => document.querySelectorAll(\"div\").length"}\nexit' | timeout 30 mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

**⚡ Pattern:** `cleanup; sleep; echo commands | timeout shell`

This avoids:
- ❌ Browser profile locks (cleanup first)
- ❌ Multiple shell sessions (one pipeline)
- ❌ Hanging commands (timeout wrapper)

## Usage

**List available tools:**
```bash
mcp tools bunx -y chrome-devtools-mcp@latest
```

**Call tools (individual commands):**
```bash
# Navigate to a page (includes page list in response)
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"url":"https://example.com"}'

# Take screenshot
mcp call take_screenshot bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"fullPage":true,"format":"png"}'

# Take snapshot (page content as text)
mcp call take_snapshot bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"verbose":false}'

# List console messages
mcp call list_console_messages bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"pageIdx":0}'

# Execute JavaScript
mcp call evaluate_script bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"function":"() => document.title"}'
```

**Interactive shell mode (RECOMMENDED - maintains single browser instance):**
```bash
mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated

# Then run commands:
navigate_page {"url":"https://example.com"}
take_snapshot {"verbose":false}
list_console_messages {"pageIdx":0}
new_page {"url":"https://httpbin.org"}
exit
```

**With Chrome launch options:**
```bash
# Headless mode
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --headless --isolated --params '{"url":"https://example.com"}'

# Custom viewport
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --viewport "1920x1080" --isolated --params '{"url":"https://example.com"}'

# Connect to existing Chrome instance (no --isolated needed)
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --browserUrl http://127.0.0.1:9222 --params '{"url":"https://example.com"}'
```

## Common Workflows

**Check localhost console logs:**
```bash
# Shell mode (RECOMMENDED):
mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
# Then: navigate_page {"url":"http://localhost:3000"}
# Then: list_console_messages {"pageIdx":0}

# Or as individual commands:
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"url":"http://localhost:3000"}'
mcp call list_console_messages bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"pageIdx":0}'
```

**Automate form filling:**
```bash
mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
# Then in shell:
# navigate_page {"url":"https://example.com/login"}
# take_snapshot {"verbose":false}   # Get UIDs for elements
# fill {"uid":"#username","value":"user"}
# fill {"uid":"#password","value":"pass"}
# click {"uid":"#submit"}
```

**Network debugging:**
```bash
# Shell mode (RECOMMENDED):
mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
# Then: navigate_page {"url":"https://example.com"}
# Then: list_network_requests {"pageIdx":0}

# Or as individual commands:
mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"url":"https://example.com"}'
mcp call list_network_requests bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"pageIdx":0}'
```

## Key Tools

- **navigate_page** - Go to URL (returns page list)
- **new_page** - Open new tab (returns page list)
- **select_page** - Switch to different page by index
- **close_page** - Close page by index
- **click** - Click element
- **fill** - Fill input/textarea
- **evaluate_script** - Run JavaScript
- **take_screenshot** - Capture page as image
- **take_snapshot** - Get page content as text with UIDs
- **list_console_messages** - View console logs (use `{"pageIdx":0}`)
- **list_network_requests** - View network activity (use `{"pageIdx":0}`)
- **wait_for** - Wait for text/condition

## Important Notes

- Always use `bunx` (not `npx`) for chrome-devtools-mcp
- **Correct syntax:** `mcp call TOOL_NAME bunx -y chrome-devtools-mcp@latest -- --isolated --params '{...}'`
  - Server command comes AFTER tool name, BEFORE --params
  - Parameters are passed directly (no "arguments" wrapper)
  - Use `-- --isolated` to create temporary profile (prevents browser lock conflicts)
- Server exposes full browser content - avoid sensitive data

## Working with Multiple Commands

**Problem:** Each `mcp call` starts a new server & browser instance, causing conflicts.

**Solutions:**

1. **Shell mode (RECOMMENDED):** Maintains single browser instance
   ```bash
   mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
   ```

2. **Individual calls:** Use `-- --isolated` for one-off commands
   ```bash
   mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --isolated --params '{"url":"..."}'
   ```

3. **Connect to running Chrome:** Start Chrome with debugging enabled
   ```bash
   /Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome --remote-debugging-port=9222
   mcp call navigate_page bunx -y chrome-devtools-mcp@latest -- --browserUrl http://127.0.0.1:9222 --params '{"url":"..."}'
   ```

## Known Issues (mcp CLI v0.7.1)

⚠️ **Bug:** Tools with empty parameter schemas fail with "Invalid arguments" error.

**Workaround:** Provide at least one optional parameter:
- ✅ `list_console_messages {"pageIdx":0}` - Works
- ✅ `list_network_requests {"pageIdx":0}` - Works
- ✅ `take_snapshot {"verbose":false}` - Works
- ❌ `list_pages` - Broken, use `navigate_page` or `new_page` instead (they return page list)

## Troubleshooting

**Problem: "The browser is already running" error**

This happens when a previous Chrome instance is still holding the profile lock.

**Quick fix (ALWAYS DO THIS FIRST):**
```bash
pkill -9 -f "chrome-devtools-mcp" 2>/dev/null; sleep 1
```

**Then run your command:**
```bash
echo -e 'navigate_page {"url":"YOUR_URL"}\nlist_console_messages {"pageIdx":0}\nexit' | mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

**Problem: Multiple failed attempts**

Don't create multiple shell sessions - keep ONE session open and run multiple commands:

❌ **BAD (slow - 2 separate sessions):**
```bash
echo 'navigate_page {"url":"..."}' | mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
echo 'list_console_messages {"pageIdx":0}' | mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

✅ **GOOD (fast - 1 session, multiple commands):**
```bash
echo -e 'navigate_page {"url":"..."}\nlist_console_messages {"pageIdx":0}\nexit' | mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```

**Problem: Commands hanging/timing out**

Use `timeout` to prevent hanging:
```bash
timeout 30 mcp shell bunx -y chrome-devtools-mcp@latest -- --isolated
```