Chrome Devtools

---
name: chrome-devtools
description: Browser automation, debugging, and performance analysis using Puppeteer CLI scripts. Use for automating browsers, taking screenshots, analyzing performance, monitoring network traffic, web scraping, form automation, and JavaScript debugging.
license: Apache-2.0
---

# Chrome DevTools Agent Skill

Browser automation via executable Puppeteer scripts. All scripts output JSON for easy parsing.

## Quick Start

### Installation

#### Step 1: Install System Dependencies (Linux/WSL only)

On Linux/WSL, Chrome requires system libraries. Install them first:

```bash
cd .claude/skills/chrome-devtools/scripts
./install-deps.sh  # Auto-detects OS and installs required libs
```

Supports: Ubuntu, Debian, Fedora, RHEL, CentOS, Arch, Manjaro

**macOS/Windows**: Skip this step (dependencies bundled with Chrome)

#### Step 2: Install Node Dependencies

```bash
npm install  # Installs puppeteer, debug, yargs
```

### Test
```bash
node navigate.js --url https://example.com
# Output: {"success": true, "url": "https://example.com", "title": "Example Domain"}
```

## Available Scripts

All scripts are in `.claude/skills/chrome-devtools/scripts/`

### Script Usage
- `./scripts/README.md`

### Core Automation
- `navigate.js` - Navigate to URLs
- `screenshot.js` - Capture screenshots (full page or element)
- `click.js` - Click elements
- `fill.js` - Fill form fields
- `evaluate.js` - Execute JavaScript in page context

### Analysis & Monitoring
- `snapshot.js` - Extract interactive elements with metadata
- `console.js` - Monitor console messages/errors
- `network.js` - Track HTTP requests/responses
- `performance.js` - Measure Core Web Vitals + record traces

## Usage Patterns

### Single Command
```bash
cd .claude/skills/chrome-devtools/scripts
node screenshot.js --url https://example.com --output ./docs/screenshots/page.png
```
**Important**: Always save screenshots to `./docs/screenshots` directory.

### Chain Commands (reuse browser)
```bash
# Keep browser open with --close false
node navigate.js --url https://example.com/login --close false
node fill.js --selector "#email" --value "user@example.com" --close false
node fill.js --selector "#password" --value "secret" --close false
node click.js --selector "button[type=submit]"
```

### Parse JSON Output
```bash
# Extract specific fields with jq
node performance.js --url https://example.com | jq '.vitals.LCP'

# Save to file
node network.js --url https://example.com --output /tmp/requests.json
```

## Common Workflows

### Web Scraping
```bash
node evaluate.js --url https://example.com --script "
  Array.from(document.querySelectorAll('.item')).map(el => ({
    title: el.querySelector('h2')?.textContent,
    link: el.querySelector('a')?.href
  }))
" | jq '.result'
```

### Performance Testing
```bash
PERF=$(node performance.js --url https://example.com)
LCP=$(echo $PERF | jq '.vitals.LCP')
if (( $(echo "$LCP < 2500" | bc -l) )); then
  echo "✓ LCP passed: ${LCP}ms"
else
  echo "✗ LCP failed: ${LCP}ms"
fi
```

### Form Automation
```bash
node fill.js --url https://example.com --selector "#search" --value "query" --close false
node click.js --selector "button[type=submit]"
```

### Error Monitoring
```bash
node console.js --url https://example.com --types error,warn --duration 5000 | jq '.messageCount'
```

## Script Options

All scripts support:
- `--headless false` - Show browser window
- `--close false` - Keep browser open for chaining
- `--timeout 30000` - Set timeout (milliseconds)
- `--wait-until networkidle2` - Wait strategy

See `./scripts/README.md` for complete options.

## Output Format

All scripts output JSON to stdout:
```json
{
  "success": true,
  "url": "https://example.com",
  ... // script-specific data
}
```

Errors go to stderr:
```json
{
  "success": false,
  "error": "Error message"
}
```

## Finding Elements

Use `snapshot.js` to discover selectors:
```bash
node snapshot.js --url https://example.com | jq '.elements[] | {tagName, text, selector}'
```

## Troubleshooting

### Common Errors

**"Cannot find package 'puppeteer'"**
- Run: `npm install` in the scripts directory

**"error while loading shared libraries: libnss3.so"** (Linux/WSL)
- Missing system dependencies
- Fix: Run `./install-deps.sh` in scripts directory
- Manual install: `sudo apt-get install -y libnss3 libnspr4 libasound2t64 libatk1.0-0 libatk-bridge2.0-0 libcups2 libdrm2 libxkbcommon0 libxcomposite1 libxdamage1 libxfixes3 libxrandr2 libgbm1`

**"Failed to launch the browser process"**
- Check system dependencies installed (Linux/WSL)
- Verify Chrome downloaded: `ls ~/.cache/puppeteer`
- Try: `npm rebuild` then `npm install`

**Chrome not found**
- Puppeteer auto-downloads Chrome during `npm install`
- If failed, manually trigger: `npx puppeteer browsers install chrome`

### Script Issues

**Element not found**
- Get snapshot first to find correct selector: `node snapshot.js --url <url>`

**Script hangs**
- Increase timeout: `--timeout 60000`
- Change wait strategy: `--wait-until load` or `--wait-until domcontentloaded`

**Blank screenshot**
- Wait for page load: `--wait-until networkidle2`
- Increase timeout: `--timeout 30000`

**Permission denied on scripts**
- Make executable: `chmod +x *.sh`

## Reference Documentation

Detailed guides available in `./references/`:
- [CDP Domains Reference](./references/cdp-domains.md) - 47 Chrome DevTools Protocol domains
- [Puppeteer Quick Reference](./references/puppeteer-reference.md) - Complete Puppeteer API patterns
- [Performance Analysis Guide](./references/performance-guide.md) - Core Web Vitals optimization

## Advanced Usage

### Custom Scripts
Create custom scripts using shared library:
```javascript
import { getBrowser, getPage, closeBrowser, outputJSON } from './lib/browser.js';
// Your automation logic
```

### Direct CDP Access
```javascript
const client = await page.createCDPSession();
await client.send('Emulation.setCPUThrottlingRate', { rate: 4 });
```

See reference documentation for advanced patterns and complete API coverage.

## External Resources

- [Puppeteer Documentation](https://pptr.dev/)
- [Chrome DevTools Protocol](https://chromedevtools.github.io/devtools-protocol/)
- [Scripts README](./scripts/README.md)