webapp-testing

Toolkit for interacting with and testing local web applications using Playwright. Supports verifying frontend functionality, debugging UI behavior, capturing browser screenshots, and viewing browser logs.

Complete terms in LICENSE.txtSource: anthropics/skills

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Web Application Testing

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

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:

bash

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

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

bash

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):

python

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

Inspect rendered DOM: ``python page.screenshot(path='/tmp/inspect.png', full_page=True) content = page.content() page.locator('button').all() ``
Identify selectors from inspection results
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 Files

examples/ - Examples showing common patterns:
- element_discovery.py - Discovering buttons, links, and inputs on a page
- static_html_automation.py - Using file:// URLs for local HTML
- console_logging.py - Capturing console logs during automation

Bundle files

Files included in the skill's folder on GitHub. Only SKILL.md is hosted here — get the full bundle from the source repository.

LICENSE.txt
SKILL.md
examples/console_logging.py
examples/element_discovery.py
examples/static_html_automation.py
scripts/with_server.py