Web Application Testing

To test local web applications, write native Python Playwright scripts.

Triggers

Activate this skill when the user wants to:

• Verify frontend functionality of a local web application
• Debug UI behavior or capture browser screenshots
• Automate browser interactions (form fills, button clicks, navigation)
• View browser console logs or test rendering
• Write Playwright automation scripts for local dev environments

NOT For

• Production testing — do not run against live production URLs; use staging only
• Load testing or performance testing — use dedicated tools (k6, Locust, etc.)
• API-only testing — no browser needed; use

  exec

  with curl or httpx
• Visual regression testing at scale — this skill handles functional automation, not pixel-diffing

---

Helper Scripts Available:

• scripts/with_server.py

  - Manages server lifecycle (supports multiple servers)

Always run scripts with

--help

first to see usage. DO NOT read the source until you try running the script first and find that a customized solution is abslutely necessary. These scripts can be very large and thus pollute your context window. They exist to be called directly as black-box scripts rather than ingested into your context window.

Decision Tree: Choosing Your Approach

User task → Is it static HTML?
    ├─ Yes → Read HTML file directly to identify selectors
    │         ├─ Success → Write Playwright script using selectors
    │         └─ Fails/Incomplete → Treat as dynamic (below)
    │
    └─ No (dynamic webapp) → Is the server already running?
        ├─ No → Run: python scripts/with_server.py --help
        │        Then use the helper + write simplified Playwright script
        │
        └─ Yes → Reconnaissance-then-action:
            1. Navigate and wait for networkidle
            2. Take screenshot or inspect DOM
            3. Identify selectors from rendered state
            4. Execute actions with discovered selectors

Example: Using with_server.py

To start a server, run

--help

first, then use the helper:

Single server:

python scripts/with_server.py --server "npm run dev" --port 5173 -- python your_automation.py

Multiple servers (e.g., backend + frontend):

python scripts/with_server.py \
  --server "cd backend && python server.py" --port 3000 \
  --server "cd frontend && npm run dev" --port 5173 \
  -- python your_automation.py

To create an automation script, include only Playwright logic (servers are managed automatically):

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True) # Always launch chromium in headless mode
    page = browser.new_page()
    page.goto('http://localhost:5173') # Server already running and ready
    page.wait_for_load_state('networkidle') # CRITICAL: Wait for JS to execute
    # ... your automation logic
    browser.close()

Reconnaissance-Then-Action Pattern

1. Inspect rendered DOM:

   page.screenshot(path='/tmp/inspect.png', full_page=True)
   content = page.content()
   page.locator('button').all()
   

2. Identify selectors from inspection results

3. Execute actions using discovered selectors

Common Pitfall

❌ Don't inspect the DOM before waiting for

networkidle

on dynamic apps ✅ Do wait for

page.wait_for_load_state('networkidle')

before inspection

Best Practices

• Use bundled scripts as black boxes - To accomplish a task, consider whether one of the scripts available in

  scripts/

  can help. These scripts handle common, complex workflows reliably without cluttering the context window. Use

  --help

  to see usage, then invoke directly.
• Use

  sync_playwright()

  for synchronous scripts
• Always close the browser when done
• Use descriptive selectors:

  text=

  ,

  role=

  , CSS selectors, or IDs
• Add appropriate waits:

  page.wait_for_selector()

  or

  page.wait_for_timeout()

Reference

The

scripts/with_server.py

helper is the primary bundled utility. Check

scripts/

for any other available helpers before writing custom code.