Playwright Web Automation

Browser automation via Chromium + playwright-core over CDP. No MCP server needed — scripts run as .mjs files.

Prerequisites

# Install playwright-core (no browser download — uses existing Chromium)
npm install playwright-core

# Verify Chromium exists
which chromium || ls /Applications/Chromium.app/Contents/MacOS/Chromium

Launch Chromium with CDP

# Kill any existing debug instance
pkill -f "remote-debugging-port=9222" 2>/dev/null

# Launch headless (cron/CI) or headed (interactive)
chromium --remote-debugging-port=9222 \
  --user-data-dir="/tmp/playwright-profile" \
  --disable-blink-features=AutomationControlled \
  --no-first-run --no-default-browser-check \
  --headless=new \
  "about:blank" > /tmp/chromium.log 2>&1 &

# macOS: use full path /Applications/Chromium.app/Contents/MacOS/Chromium
# Linux: chromium-browser or chromium

# Wait for CDP
sleep 3 && curl -sf http://localhost:9222/json/version > /dev/null && echo "CDP ready"

Connect via Playwright (ESM)

Write scripts as .mjs files:

// run: node script.mjs
import { chromium } from 'playwright-core';

const browser = await chromium.connectOverCDP('http://localhost:9222');
const ctx = browser.contexts()[0];
const page = ctx.pages()[0] || await ctx.newPage();

await page.goto('https://example.com', { waitUntil: 'domcontentloaded', timeout: 15000 });
await page.waitForTimeout(2000);
await page.screenshot({ path: '/tmp/screenshot.png' });

await browser.close(); // disconnects, doesn't kill Chromium

IMPORTANT: Always use .mjs extension — playwright-core is ESM-only.

Key Patterns

Screenshot & Inspect

await page.screenshot({ path: '/tmp/screen.png' });
// Read /tmp/screen.png in Claude to see it visually

Fill Forms & Click

// Inspect inputs first
const inputs = await page.evaluate(() =>
  Array.from(document.querySelectorAll('input')).map(i => ({
    name: i.name, type: i.type, placeholder: i.placeholder
  }))
);
console.log(JSON.stringify(inputs, null, 2));

await page.fill('input[name="email"]', 'user@example.com');
await page.click('button:has-text("Submit")');
await page.waitForTimeout(2000);

Extract Page Content

const text = await page.evaluate(() => document.body.innerText);
const html = await page.content();
const title = await page.title();

Wait for Navigation

await Promise.all([
  page.waitForNavigation({ waitUntil: 'networkidle' }),
  page.click('button:has-text("Login")')
]);

SPA / Client-Side Rendered Data

SPAs may not hydrate fully in headless. Use data endpoints if available:

const data = await page.evaluate(async () => {
  const res = await fetch('/api/data', { credentials: 'include' });
  return res.json();
});

Multi-Page Flow

await page.goto('https://app.example.com/login');
await page.fill('#email', 'user@example.com');
await page.fill('#password', 'password');
await page.click('button[type="submit"]');
await page.waitForNavigation({ waitUntil: 'networkidle' });
await page.screenshot({ path: '/tmp/after-login.png' });

// Continue to next page
await page.click('a:has-text("Dashboard")');
await page.waitForLoadState('networkidle');
await page.screenshot({ path: '/tmp/dashboard.png' });

Record Video

// Must create a NEW context for video recording
const ctx = await browser.newContext({
  recordVideo: { dir: '/tmp/videos/', size: { width: 1280, height: 720 } }
});
const page = await ctx.newPage();
await page.goto('https://example.com');
// ... do things ...
await ctx.close(); // video saved to /tmp/videos/*.webm

Console & Network Monitoring

page.on('console', msg => console.log(`[${msg.type()}] ${msg.text()}`));
page.on('response', res => {
  if (res.status() >= 400) console.log(`[${res.status()}] ${res.url()}`);
});

Selectors (prefer in this order)

1. data-testid="foo" — page.click('[data-testid="foo"]')
2. Role — page.getByRole('button', { name: 'Submit' })
3. Text — page.click('button:has-text("Submit")')
4. CSS — page.click('.submit-btn') (fragile, last resort)

Cleanup

pkill -f "remote-debugging-port=9222"

Troubleshooting

Problem	Solution
CDP not responding	Wait longer, check curl http://localhost:9222/json/version
Port 9222 in use	pkill -f "remote-debugging-port=9222" then relaunch
ESM import error	Use .mjs extension, not .js
Page not loading	Increase timeout, use waitUntil: 'domcontentloaded'
Screenshots blank	Add page.waitForTimeout(2000) before capture
CSS not loaded	Use waitUntil: 'networkidle' or wait for a visible element
Form submit fails	Check if element is visible: await el.isVisible()