Playwright MCP

Playwright MCP

Browser automation for visual verification. Self-check UI before delivering.

When to Use

• After creating/​modifying components → verify render
• Before delivering code → final QA check
• Debugging UI issues → see actual browser state
• Responsive testing → check mobile/​tablet/​desktop

Process

NAVIGATE → VERIFY → FIX → DELIVER

1. Start dev server: npm run dev
2. browser_navigate → open page
3. browser_take_screenshot → visual check
4. browser_console_messages { onlyErrors: true } → MUST BE EMPTY
5. Fix issues if any → repeat
6. Deliver when clean

Tools Quick Reference

Navigation:
  browser_navigate:      { url: "http://localhost:3000" }
  browser_resize:        { width: 375, height: 812 }
  browser_wait_for:      { time: 2 } | { text: "Success" }
  browser_close:         {}

Inspection:
  browser_snapshot:           # Get element refs for interactions
  browser_take_screenshot:    { filename: "check.png", fullPage: true }
  browser_console_messages:   { onlyErrors: true }  # CRITICAL
  browser_network_requests:   {}
  browser_evaluate:           { function: "() => ..." }

Interaction:
  browser_click:   { element: "Submit button", ref: "e5" }
  browser_type:    { element: "Email input", ref: "e3", text: "[email protected]" }
  browser_hover:   { element: "Menu item", ref: "e8" }

Pre-Delivery Checklist

MUST PASS before delivery:
  ✓ browser_take_screenshot → looks correct
  ✓ browser_console_messages { onlyErrors: true } → EMPTY
  ✓ browser_network_requests → no 4xx/​5xx
  ✓ Mobile viewport (375px) works

Common Workflows

Quick Verification

browser_navigate → browser_take_screenshot → browser_console_messages { onlyErrors: true }

Responsive Test

browser_resize { width: 375, height: 812 }  → screenshot
browser_resize { width: 768, height: 1024 } → screenshot
browser_resize { width: 1440, height: 900 } → screenshot

Form Test

browser_snapshot              # get refs
browser_type { ref, text }    # fill fields
browser_click { ref }         # submit
browser_wait_for { text }     # wait for result
browser_console_messages      # check errors

Common Console Errors

"Hydration mismatch":
  → Server/​client render different
  → Fix: 'use client', useEffect for browser-only code

"Cannot read property of undefined":
  → Data not loaded
  → Fix: optional chaining, loading states

"Failed to fetch":
  → API error
  → Check: browser_network_requests for details

Viewport Sizes

Mobile:     { width: 375, height: 812 }   # iPhone
Tablet:     { width: 768, height: 1024 }  # iPad
Laptop:     { width: 1366, height: 768 }
Desktop:    { width: 1440, height: 900 }
Full HD:    { width: 1920, height: 1080 }

References

• tools.md — Full MCP tools documentation with all parameters
• workflows.md — Ready-to-use verification scenarios