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