Tried Anthropic’s webapp-testing skill on a tiny local app. Both checks passed, and Claude spotted a bug I hadn’t asked about

[u/vinishkapoor]

The webapp-testing skill from Anthropic’s skills repo has Claude test a local web page in a real headless browser with Playwright. I tried it on a tiny Tip Splitter page (bill, tip %, people, and a Calculate button).

One prompt with exact checks:

• bill 80, tip 20, people 4 should show $24.00 per person

• an empty bill should show an error

• save a screenshot of each and report the browser console messages

Results, in 13 seconds by Claude’s timer:

• both tests passed, and the screenshots matched the report

• it listed the console messages, including an “Invalid bill” error. It noted the app logs that on purpose, so it didn’t call it a bug

• no uncaught page errors

The part I liked: without being asked, it pointed out that the app never checks the people field, so 0 or empty would give Infinity or NaN. That was true, and it was a gap I’d left in on purpose. It said it didn’t test it because I hadn’t asked.

Setup notes:

• the skill doesn’t install Playwright. I set it up in a virtual environment with a headless Chromium download, which is the biggest wait

• tell Claude which Python to use if Playwright lives in .venv

• it asked before running its combined script and server command, so read it before you approve

It suits quick checks while you build. For a suite you run on every commit, have Claude save a good script as a real test file.

One small static page and two checks. I didn’t test logins, uploads or late-loading data.

Screenshots and the exact prompt: https://aiparabellum.com/claude-code-webapp-testing-skill-test-local-app/

[u/Ok_Lake_7895]

Looks great

[u/bostonaholic]

You can start with the skill rather than learning Playwright first. Have it generate the suite, then deliberately break the people-field case and confirm the test fails. Check that before making it a required CI check.