Chrome DevTools Agent Skill

Browser automation via Puppeteer scripts with persistent sessions. All scripts output JSON.

Skill Location

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope.

# Detect skill location (no cd needed - scripts use __dirname for paths)
SKILL_DIR=""
if [ -d ".claude/skills/chrome-devtools/scripts" ]; then
  SKILL_DIR=".claude/skills/chrome-devtools/scripts"
elif [ -d "$HOME/.claude/skills/chrome-devtools/scripts" ]; then
  SKILL_DIR="$HOME/.claude/skills/chrome-devtools/scripts"
fi
# Run scripts with full path: node "$SKILL_DIR/script.js" --args

Choosing Your Approach

Scenario	Approach
Source-available sites	Read source code first, write selectors directly
Unknown layouts	Use `aria-snapshot.js` for semantic discovery
Visual inspection	Take screenshots to verify rendering
Debug issues	Collect console logs, analyze with session storage
Accessibility audit	Use ARIA snapshot for semantic structure analysis

Automation Browsing Running Mode

Detect current OS and launch browser as headless only when running on Linux, WSL, or CI environments.
For macOS/Windows, browser always runs in headed mode for better debugging.
Run multiple scripts/sessions in parallel to simulate real user interactions.
Run multiple scripts/sessions in parallel to simulate different device types (mobile, tablet, desktop).
Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope.

ARIA Snapshot (Element Discovery)

When page structure is unknown, use aria-snapshot.js to get a YAML-formatted accessibility tree with semantic roles, accessible names, states, and stable element references.

Get ARIA Snapshot

# Generate ARIA snapshot and output to stdout
node "$SKILL_DIR/aria-snapshot.js" --url https://example.com

# Save to file in snapshots directory
node "$SKILL_DIR/aria-snapshot.js" --url https://example.com --output ./.claude/chrome-devtools/snapshots/page.yaml

Example YAML Output

- banner:
  - link "Hacker News" [ref=e1]
    /url: https://news.ycombinator.com
  - navigation:
    - link "new" [ref=e2]
    - link "past" [ref=e3]
    - link "comments" [ref=e4]
- main:
  - list:
    - listitem:
      - link "Show HN: My new project" [ref=e8]
      - text: "128 points by user 3 hours ago"
- contentinfo:
  - textbox [ref=e10]
    /placeholder: "Search"

Interpreting ARIA Notation

Notation	Meaning
`[ref=eN]`	Stable identifier for interactive elements
`[checked]`	Checkbox/radio is selected
`[disabled]`	Element is inactive
`[expanded]`	Accordion/dropdown is open
`[level=N]`	Heading hierarchy (1-6)
`/url:`	Link destination
`/placeholder:`	Input placeholder text
`/value:`	Current input value

Interact by Ref

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. Use select-ref.js to interact with elements by their ref:

# Click element with ref e5
node "$SKILL_DIR/select-ref.js" --ref e5 --action click

# Fill input with ref e10
node "$SKILL_DIR/select-ref.js" --ref e10 --action fill --value "search query"

# Get text content
node "$SKILL_DIR/select-ref.js" --ref e8 --action text

# Screenshot specific element
node "$SKILL_DIR/select-ref.js" --ref e1 --action screenshot --output ./logo.png

# Focus element
node "$SKILL_DIR/select-ref.js" --ref e10 --action focus

# Hover over element
node "$SKILL_DIR/select-ref.js" --ref e5 --action hover

Store Snapshots

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. Store snapshots for analysis in <project>/.claude/chrome-devtools/snapshots/:

# Create snapshots directory
mkdir -p .claude/chrome-devtools/snapshots

# Capture and store with timestamp
SESSION="$(date +%Y%m%d-%H%M%S)"
node "$SKILL_DIR/aria-snapshot.js" --url https://example.com --output .claude/chrome-devtools/snapshots/$SESSION.yaml

Workflow: Unknown Page Structure

Get snapshot to discover elements:

node "$SKILL_DIR/aria-snapshot.js" --url https://example.com

Identify target from YAML output (e.g., [ref=e5] for a button)

Interact by ref:

node "$SKILL_DIR/select-ref.js" --ref e5 --action click

Verify result with screenshot or new snapshot:

node "$SKILL_DIR/screenshot.js" --output ./result.png

Local HTML Files

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. IMPORTANT: Never browse local HTML files via file:// protocol. Always serve via local server: Why: file:// protocol blocks many browser features (CORS, ES modules, fetch API, service workers). Local server ensures proper HTTP behavior.

# Option 1: npx serve (recommended)
npx serve ./dist -p 3000 &
node "$SKILL_DIR/navigate.js" --url http://localhost:3000

# Option 2: Python http.server
python -m http.server 3000 --directory ./dist &
node "$SKILL_DIR/navigate.js" --url http://localhost:3000

Note: when port 3000 is busy, find an available port with lsof -i :3000 and use a different one.

Quick Start

# Install dependencies (one-time setup)
npm install --prefix "$SKILL_DIR"

# Test (browser stays running for session reuse)
node "$SKILL_DIR/navigate.js" --url https://example.com
# Output: {"success": true, "url": "...", "title": "..."}

Linux/WSL only: Run "$SKILL_DIR/install-deps.sh" first for Chrome system libraries.

Session Persistence

Browser state persists across script executions via WebSocket endpoint file (.browser-session.json).

Default behavior: Scripts disconnect but keep browser running for session reuse.

# First script: launches browser, navigates, disconnects (browser stays running)
node "$SKILL_DIR/navigate.js" --url https://example.com/login

# Subsequent scripts: connect to existing browser, reuse page state
node "$SKILL_DIR/fill.js" --selector "#email" --value "user@example.com"
node "$SKILL_DIR/fill.js" --selector "#password" --value "secret"
node "$SKILL_DIR/click.js" --selector "button[type=submit]"

# Close browser when done
node "$SKILL_DIR/navigate.js" --url about:blank --close true

Session management:

--close true: Close browser and clear session
Default (no flag): Keep browser running for next script

Available Scripts

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. All in .claude/skills/chrome-devtools/scripts/:

Script	Purpose
`navigate.js`	Navigate to URLs
`screenshot.js`	Capture screenshots (auto-compress >5MB via Sharp)
`click.js`	Click elements
`fill.js`	Fill form fields
`evaluate.js`	Execute JS in page context
`snapshot.js`	Extract interactive elements (JSON format)
`aria-snapshot.js`	Get ARIA accessibility tree (YAML format with refs)
`select-ref.js`	Interact with elements by ref from ARIA snapshot
`console.js`	Monitor console messages/errors
`network.js`	Track HTTP requests/responses
`performance.js`	Measure Core Web Vitals
`ws-debug.js`	Debug WebSocket connections (basic)
`ws-full-debug.js`	Debug WebSocket with full events/frames

Workflow Loop

Execute focused script for single task
Observe JSON output
Assess completion status
Decide next action
Repeat until done

Writing Custom Test Scripts

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. For complex automation, write scripts to <project>/.claude/chrome-devtools/tmp/:

# Create tmp directory for test scripts
mkdir -p $SKILL_DIR/.claude/chrome-devtools/tmp

# Write a test script
cat > $SKILL_DIR/.claude/chrome-devtools/tmp/login-test.js << 'EOF'
import { getBrowser, getPage, disconnectBrowser, outputJSON } from '../scripts/lib/browser.js';

async function loginTest() {
  const browser = await getBrowser();
  const page = await getPage(browser);

  await page.goto('https://example.com/login');
  await page.type('#email', 'user@example.com');
  await page.type('#password', 'secret');
  await page.click('button[type=submit]');
  await page.waitForNavigation();

  outputJSON({
    success: true,
    url: page.url(),
    title: await page.title()
  });

  await disconnectBrowser();
}

loginTest();
EOF

# Run the test
node $SKILL_DIR/.claude/chrome-devtools/tmp/login-test.js

Key principles for custom scripts:

Single-purpose: one script, one task
Always call disconnectBrowser() at the end (keeps browser running)
Use closeBrowser() only when ending session completely
Output JSON for easy parsing
Plain JavaScript only in page.evaluate() callbacks

Screenshots

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. Store screenshots for analysis in <project>/.claude/chrome-devtools/screenshots/:

# Basic screenshot
node "$SKILL_DIR/screenshot.js" --url https://example.com --output ./.claude/chrome-devtools/screenshots/page.png

# Full page
node "$SKILL_DIR/screenshot.js" --url https://example.com --output ./.claude/chrome-devtools/screenshots/page.png --full-page true

# Specific element
node "$SKILL_DIR/screenshot.js" --url https://example.com --selector ".main-content" --output ./.claude/chrome-devtools/screenshots/element.png

Auto-Compression (Sharp)

Screenshots >5MB auto-compress using Sharp (4-5x faster than ImageMagick):

# Default: compress if >5MB
node "$SKILL_DIR/screenshot.js" --url https://example.com --output ./.claude/chrome-devtools/screenshots/page.png

# Custom threshold (3MB)
node "$SKILL_DIR/screenshot.js" --url https://example.com --output ./.claude/chrome-devtools/screenshots/page.png --max-size 3

# Disable compression
node "$SKILL_DIR/screenshot.js" --url https://example.com --output ./.claude/chrome-devtools/screenshots/page.png --no-compress

Store screenshots for analysis in <project>/.claude/chrome-devtools/screenshots/.

Console Log Collection & Analysis

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope.

Capture Logs

# Capture all logs for 10 seconds
node "$SKILL_DIR/console.js" --url https://example.com --duration 10000

# Filter by type
node "$SKILL_DIR/console.js" --url https://example.com --types error,warn --duration 5000

Session Storage Pattern

Store logs for analysis in <project>/.claude/chrome-devtools/logs/<session>/:

# Create session directory
SESSION="$(date +%Y%m%d-%H%M%S)"
mkdir -p .claude/chrome-devtools/logs/$SESSION

# Capture and store
node "$SKILL_DIR/console.js" --url https://example.com --duration 10000 > .claude/chrome-devtools/logs/$SESSION/console.json
node "$SKILL_DIR/network.js" --url https://example.com > .claude/chrome-devtools/logs/$SESSION/network.json

# View errors
jq '.messages[] | select(.type=="error")' .claude/chrome-devtools/logs/$SESSION/console.json

Root Cause Analysis

# 1. Check for JavaScript errors
node "$SKILL_DIR/console.js" --url https://example.com --types error,pageerror --duration 5000 | jq '.messages'

# 2. Correlate with network failures
node "$SKILL_DIR/network.js" --url https://example.com | jq '.requests[] | select(.response.status >= 400)'

# 3. Check specific error stack traces
node "$SKILL_DIR/console.js" --url https://example.com --types error --duration 5000 | jq '.messages[].stack'

Finding Elements

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. Use snapshot.js to discover selectors before interacting:

# Get all interactive elements
node "$SKILL_DIR/snapshot.js" --url https://example.com | jq '.elements[] | {tagName, text, selector}'

# Find buttons
node "$SKILL_DIR/snapshot.js" --url https://example.com | jq '.elements[] | select(.tagName=="button")'

# Find by text content
node "$SKILL_DIR/snapshot.js" --url https://example.com | jq '.elements[] | select(.text | contains("Submit"))'

Error Recovery

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope. If script fails:

# 1. Capture current state (without navigating to preserve state)
node "$SKILL_DIR/screenshot.js" --output ./.claude/skills/chrome-devtools/screenshots/debug.png

# 2. Get console errors
node "$SKILL_DIR/console.js" --url about:blank --types error --duration 1000

# 3. Discover correct selector
node "$SKILL_DIR/snapshot.js" | jq '.elements[] | select(.text | contains("Submit"))'

# 4. Try XPath if CSS fails
node "$SKILL_DIR/click.js" --selector "//button[contains(text(),'Submit')]"

Common Patterns

Web Scraping

node "$SKILL_DIR/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'

Form Automation

node "$SKILL_DIR/navigate.js" --url https://example.com/form
node "$SKILL_DIR/fill.js" --selector "#search" --value "query"
node "$SKILL_DIR/click.js" --selector "button[type=submit]"

Performance Testing

node "$SKILL_DIR/performance.js" --url https://example.com | jq '.vitals'

Script Options

All scripts support:

--headless false - Show browser window
--close true - Close browser completely (default: stay running)
--timeout 30000 - Set timeout (ms)
--wait-until networkidle2 - Wait strategy Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope.

Troubleshooting

Skills can exist in project-scope or user-scope. Priority: project-scope > user-scope.

Error	Solution
`Cannot find package 'puppeteer'`	Run `npm install` in scripts directory
`libnss3.so` missing (Linux)	Run `./install-deps.sh`
Element not found	Use `snapshot.js` to find correct selector
Script hangs	Use `--timeout 60000` or `--wait-until load`
Screenshot >5MB	Auto-compressed; use `--max-size 3` for lower
Session stale	Delete `.browser-session.json` and retry

Screenshot Analysis: Missing Images

If images don't appear in screenshots, they may be waiting for animation triggers:

Scroll-triggered animations: Scroll element into view first

node "$SKILL_DIR/evaluate.js" --script "document.querySelector('.lazy-image').scrollIntoView()"
# Wait for animation
node "$SKILL_DIR/evaluate.js" --script "await new Promise(r => setTimeout(r, 1000))"
node "$SKILL_DIR/screenshot.js" --output ./result.png

Sequential animation queue: Wait longer and retry

# First attempt
node "$SKILL_DIR/screenshot.js" --url http://localhost:3000 --output ./attempt1.png

# Wait for animations to complete
node "$SKILL_DIR/evaluate.js" --script "await new Promise(r => setTimeout(r, 2000))"

# Retry screenshot
node "$SKILL_DIR/screenshot.js" --output ./attempt2.png

Intersection Observer animations: Trigger by scrolling through page

node "$SKILL_DIR/evaluate.js" --script "window.scrollTo(0, document.body.scrollHeight)"
node "$SKILL_DIR/evaluate.js" --script "await new Promise(r => setTimeout(r, 1500))"
node "$SKILL_DIR/evaluate.js" --script "window.scrollTo(0, 0)"
node "$SKILL_DIR/screenshot.js" --output ./full-loaded.png --full-page true

Reference Documentation

./references/cdp-domains.md - Chrome DevTools Protocol domains
./references/puppeteer-reference.md - Puppeteer API patterns
./references/performance-guide.md - Core Web Vitals optimization
./scripts/README.md - Detailed script options