verifying-in-browser

Verify in Browser

Use this skill proactively after making code changes to verify the app actually works. Don't just trust that the code is correct — launch it and check.

Steps

1. Start the dev server in the background — check if one is already running by listing terminals. If not:

   npm run dev
   

   Set block_until_ms: 0 to run it in the background. Then poll until you see the "ready" message with the localhost URL.

2. Open in the side browser — launch the app beside your code:

Tool: browser_navigate
Arguments: { "url": "http://localhost:3000", "position": "side", "take_screenshot_afterwards": true }

1. Quick health check — run these three checks:

   Console errors:

   Tool: browser_console_messages
   

   Flag any errors. Warnings about deprecations can be noted but aren't blockers.

   Network failures:

   Tool: browser_network_requests
   

   Flag any 4xx/5xx responses, failed fetches, or CORS errors.

   Visual check: Review the screenshot. Does the page render? Is the layout correct? Are there any blank screens or loading spinners that never resolve?

2. Navigate to the changed page — if your changes are on a specific route, navigate there and repeat the checks.

3. Test interactions — if you changed a form, button, or interactive element:

   • Take a browser_snapshot to get element refs
   • Click, fill, or hover on the changed elements
   • Take another screenshot to verify the result

4. Report the verdict — tell the user:

   • "Verified in browser — page renders correctly, no console errors, all network requests healthy."
   • Or: "Found issues: [list of problems]"

When to Use This

• After changing any React component, CSS, or layout code
• After modifying API routes or data fetching
• After updating environment variables or configuration
• After installing or removing dependencies
• Before committing — as a final sanity check

Notes

• Use position: "side" to see code and browser at the same time.
• If the dev server is already running, skip step 1 and go straight to navigating.
• For SSR apps, check both the initial server-rendered HTML and the client-hydrated state.