Webapp Testing

---
name: webapp-testing
description: "Playwright toolkit for local web apps: navigate, click, fill forms, screenshots, console logs."
when_to_use: "Use to verify or debug frontend behavior against a dev server or static HTML."
license: Complete terms in LICENSE.txt
metadata:
  author: "Anthropic, PBC, vendored from anthropics/skills (Apache-2.0)"
  version: "1.4"
---

> Vendored from [anthropics/skills](https://github.com/anthropics/skills) under Apache-2.0. Modified: description rewrite, a Delegating section pointing at the paired `webapp-tester` agent shipped in this repo, and a tone pass (emoji and all-caps emphasis removed).

# 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. Don't read the source until the script has been run and shown not to fit the task. These scripts can be large; reading them pollutes your context window. They exist to be called directly as black boxes.

## Decision Tree: Choosing Your Approach

UI/frontend only. For pure backend/API assertions without a browser, use Playwright's request context or a plain HTTP client instead (see Limits).

```
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') # wait for JS to execute before inspecting
    # ... your automation logic
    browser.close()
```

## Reconnaissance-Then-Action Pattern

1. **Inspect rendered DOM**:
   ```python
   page.screenshot(path='/tmp/inspect.png', full_page=True)
   content = page.content()
   page.locator('button').all()
   ```
   Note: `screenshot()` only saves an image, it does not diff against a baseline (see Limits).

2. **Identify selectors** from inspection results

3. **Execute actions** using discovered selectors

## Common Pitfall

Inspecting the DOM before `networkidle` on a dynamic app reads a half-rendered page. Wait for `page.wait_for_load_state('networkidle')` first.

## 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()`

## Limits

- `screenshot()` only saves an image. There is no built-in pixel or regression diff against a baseline, wire in your own comparison (e.g. Pillow, pixelmatch) if that's needed.
- UI/frontend only. For pure backend/API assertions without a browser, use Playwright's request context (`playwright.request`) or a plain HTTP client instead.

## 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

## Delegating

To verify an app as a subagent task, spawn the `webapp-tester` agent (`agents/webapp-tester.md` in this repo). It boots through `scripts/with_server.py`, drives the flows, and returns pass/fail with screenshot + console evidence. Use this skill inline only when driving the browser yourself.