v1.3 to v1.4

---

name: webapp-testing

license: Complete terms in LICENSE.txt

metadata:

author: "Anthropic, PBC, vendored from anthropics/skills (Apache-2.0)"

---

> 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.