Web App Testing: Find Bugs Before Your Users Do

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Official Anthropic skill on GitHub

Web App Testing

Summary

Your signup form worked yesterday. Today a customer emails: "I can't create an account." The bug shipped three days ago. Nobody noticed. Now you're fixing it at 11pm.

Instead, describe what should work. Point Claude at your app, tell it what to test, and catch the broken signup before your customers do.

Testing shouldn't require a QA team or a week to set up Selenium.

Test in plain English

Describe what to test. Claude opens a real browser, clicks through the flow, and tells you what's broken—with screenshots.

Catch regressions automatically

Every feature gets a test that runs on every push. No more wondering if the last deploy broke something.

See exactly what failed

Claude walks through your critical paths and reports every failure with the page state when it broke. Know exactly where to fix it.

Pros

  • Catch bugs before they reach production—and before customers report them
  • Write tests in plain English instead of learning a test framework
  • Get screenshots of failures showing exactly what went wrong
  • Build regression tests that run before every deploy
  • Test locally, on staging, or against production URLs
  • Official Anthropic skill with real browser automation

Cons

  • Complex authentication flows with OAuth or 2FA may need additional setup for test credentials
  • Tests run against live URLs—be careful testing actions that modify production data
  • Very dynamic pages with heavy animations may need explicit wait conditions for reliable tests

How to Use Web App Testing Skill

Skill command:
1

Install the Skill

Install via the plugin marketplace, or download the skill file directly. Skills auto-activate when relevant—no manual invocation needed.

Option 1: Plugin Marketplace
/plugin marketplace add anthropics/skills
/plugin install example-skills@anthropic-agent-skills
Option 2: Direct Download
curl -o .claude/skills/webapp-testing.md https://raw.githubusercontent.com/anthropics/skills/main/skills/webapp-testing/SKILL.md
2

Point to Your App

Give Claude a URL—localhost, staging, or production. Tell it what to test in plain English. No test frameworks, no configuration files.

Example Prompt
Test http://localhost:3000 - go through the signup flow: enter an email, create a password, verify I land on the dashboard.
3

Describe the Expected Behavior

Be specific about what "working" means. Button should redirect here. Form should show this error. Page should load in under 3 seconds.

Example Prompt
/webapp-testing The cart should show the item count badge when I add a product. If I add 3 items, the badge should say "3".
4

Review the Results

Claude runs the test, reports pass or fail, and shows screenshots of what happened. Failed tests include the exact step where things went wrong.

Example Prompt
What broke on that last test? Show me the page state when the submit button failed.
5

Build Your Test Suite

Save tests for critical paths. Run them before each deploy. Catch regressions before they ship.

Example Prompt
/webapp-testing Run all tests for the checkout flow. Let me know if anything fails before I push to production.

Example Prompts

Real-world scenarios showing how to use Web App Testing effectively

Scenario: Quick smoke test before a deploy

Your Prompt

/webapp-testing http://staging.myapp.com Before I deploy, run through: (1) Homepage loads in under 3 seconds, (2) Login works with test@example.com / password123, (3) Dashboard shows recent activity. Screenshot anything that fails.

Expected Outcome

Claude runs each check, reports pass/fail for each step, and captures screenshots of any failures so you know exactly what broke.

Scenario: Testing a specific bug fix

Your Prompt

/webapp-testing http://localhost:3000/checkout Customer reported the promo code field doesn't apply discounts. Enter code SAVE20, verify the total drops by 20%, and the success message appears.

Expected Outcome

Claude applies the promo code and verifies both the price change and success message, confirming the fix works or showing exactly where it still fails.

Scenario: Form validation testing

Your Prompt

/webapp-testing Try submitting the contact form with: (1) Empty fields, (2) Invalid email format, (3) Valid inputs. Each should show the right error messages or success state.

Expected Outcome

Claude tests each validation scenario, reports whether error messages appear correctly, and confirms the happy path works as expected.

Scenario: Cross-browser compatibility check

Your Prompt

/webapp-testing Test the checkout flow on Chrome and Firefox. Flag any layout differences or broken functionality between browsers.

Expected Outcome

Claude runs the same test sequence in both browsers and reports any rendering issues, JavaScript errors, or functional differences.

Scenario: Regression testing after a refactor

Your Prompt

/webapp-testing I just refactored the auth module. Test: login, logout, password reset request, and session persistence after browser refresh. Nothing should be broken.

Expected Outcome

Claude systematically tests each auth flow, reports any regressions introduced by the refactor, and confirms which flows still work correctly.

Frequently Asked Questions

No. Claude handles the browser automation behind the scenes. You describe what to test in plain English, and Claude does the clicking, typing, and screenshot capturing. No test framework configuration required.
Yes. Include login credentials in your prompt and Claude will authenticate before running your tests. For sensitive environments, use test accounts rather than real user credentials.
You skip the test code entirely. Instead of writing JavaScript test files, you describe the test in plain English. Great for quick validation, exploratory testing, or teams without dedicated QA engineers.
Yes. Claude remembers your test descriptions. You can ask Claude to run the same tests before each deploy, building a regression suite over time without maintaining test files.
Yes. Point Claude at localhost:3000 or whatever port your dev server uses. This is ideal for testing changes before pushing to staging.
Specify in your prompt: "Test on Chrome at 1280x720" or "Test on mobile viewport." Claude will configure the browser accordingly.

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