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
- Start the dev server in the background — check if one is already running by listing terminals. If not:
npm run devSetblock_until_ms: 0to run it in the background. Then poll until you see the "ready" message with the localhost URL. - 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} - Quick health check — run these three checks: Console errors:
Tool: browser_console_messagesFlag any errors. Warnings about deprecations can be noted but aren't blockers. Network failures:Tool: browser_network_requestsFlag 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? - Navigate to the changed page — if your changes are on a specific route, navigate there and repeat the checks.
- 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
- 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.