Webapp Testing

webapp-testing

Test and debug local web applications by writing native Python Playwright scripts. The user gets verified frontend behavior, screenshots, console logs, or automation results; every server started for the job is managed, its output captured, and stopped cleanly afterwards.

This skill bundles its own steer runtime at scripts/steer.py; the commands below invoke it with python3 and need nothing installed. Paths are relative to this skill's directory: when your working directory is elsewhere (it usually is), use the skill's full path (python3 /scripts/steer.py ...).

Before you start

1. Ground yourself. Run python3 scripts/steer.py context --tools node,npm,playwright

and read the snapshot; it tells you the platform, project type, and whether node and playwright exist here before you write any script.

1. Apply past lessons. Run python3 scripts/steer.py learn show

and follow what it says; those lessons came from real previous runs.

Decision tree

User task -> Is it static HTML?
    - Yes -> Read the HTML file directly to identify selectors
             - Works -> Write a Playwright script using those selectors
             - Fails or incomplete -> Treat as dynamic (below)
    - No (dynamic webapp) -> Is the server already running?
             - No  -> Start it managed (see Servers below), then script
             - Yes -> Reconnaissance then action (below)

Servers

Start every server through steer so nothing leaks or zombies, stdout and stderr are captured to a log, and readiness is checked before your automation runs:

python3 scripts/steer.py proc start app --ready-port 5173 -- npm run dev python3 scripts/steer.py proc status app # running? port open? python3 scripts/steer.py proc logs app # captured output, e.g. startup errors python3 scripts/steer.py proc stop app # TERM then KILL, the whole process group

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

python3 scripts/steer.py proc start backend --ready-port 3000 --cwd backend -- python3 server.py python3 scripts/steer.py proc start frontend --ready-port 5173 --cwd frontend -- npm run dev

If a start fails, the error already contains the log tail: read it and fix the cause instead of retrying blindly. Always stop what you started, even when your automation failed.

Writing the automation script

Include only Playwright logic; the server is already running and ready:

from playwright.sync_api import sync_playwright

with sync_playwright() as p:
    browser = p.chromium.launch(headless=True)  # always headless
    page = browser.new_page()
    page.goto('http://localhost:5173')
    page.wait_for_load_state('networkidle')  # CRITICAL: wait for JS to execute
    # ... your automation logic
    browser.close()

Reconnaissance then action

1. Inspect the rendered DOM:

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

1. Identify selectors from what you actually saw.
2. Act using the discovered selectors.

References

Load these only when that branch of the work is hit:

• When discovering buttons, links, or inputs on a page, first read

references/element_discovery.py.

• When automating a static local HTML file (file:// URLs), first read

references/static_html_automation.py.

• When you need browser console output during automation, first read

references/console_logging.py.

Learning

This skill improves with use. As you work:

• The moment the user corrects you, or something fails and then works a

different way, capture it: python3 scripts/steer.py learn note "" --kind correction Lessons are atomic rules ("Use X not Y when Z"), never secrets.

• When a lesson from python3 scripts/steer.py learn show helped, run

python3 scripts/steer.py learn confirm ; when one was wrong, python3 scripts/steer.py learn dispute .

• Before finishing, record the outcome:

python3 scripts/steer.py learn run ok (or failed with --note).

If a learnings.md exists in this skill, read it too; those are promoted lessons that shipped with the skill.

Gotchas

• Dynamic apps render after load: never inspect the DOM before

page.wait_for_load_state('networkidle'). Empty or partial results usually mean you inspected too early.

• A server that exits right after starting: python3 scripts/steer.py proc logs app shows

why (port in use, missing dependency). Fix the cause, then start again.

• python3 scripts/steer.py proc start refuses a name that is already running; that is the

leftover server from a previous task. Stop it or reuse it deliberately.

• Prefer stable selectors: text=, role=, ids. Brittle positional

chains break on the next render.

• Use sync_playwright() for scripts and always close the browser.
• Prefer page.wait_for_selector() over arbitrary sleeps.

Source & license

This open-source skill is cataloged on AgentStack and links to its original source — we do not rehost the code.

• Author: bh-rat
• Source: bh-rat/steer
• License: MIT
• Homepage: https://steer-docs.vercel.app/

Install and usage instructions live in the source repository linked above.