JS Error Test
The JavaScript Error Checker loads any URL in headless Chrome and captures every JavaScript runtime error fired during page load and the first few seconds of interaction.
- Results in seconds
- Pass / fail + fix guidance
- No account required
The JavaScript Error Checker loads any URL in headless Chrome and captures every JavaScript runtime error fired during page load and the first few seconds of interaction. Even silent JS errors break interactions, suppress analytics, and signal a low-quality page to Google's page-experience evaluation. Catching errors before users do is a basic hygiene step that most release pipelines should automate.
What This Tool Checks
- Uncaught exceptions during page load
- Promise rejections without handlers
- Third-party script failures
- TypeErrors, ReferenceErrors and SyntaxErrors
- Network failures (failed fetch, blocked CORS)
- CSP violations recorded in console
Why It Matters for SEO
JavaScript errors break user interactions, suppress analytics events and create silent revenue leaks. Pages with frequent JS errors also signal poor quality to Google — broken pages tend to have higher bounce rates and lower engagement, both of which feed ranking signals indirectly. Most JS errors come from third parties (chat widgets, A/B testing SDKs, analytics) rather than first-party code.
How to Fix It
Wire up an error monitor (Sentry, Bugsnag, Rollbar) to capture runtime errors from real users. Add try/catch around third-party initialisation so a failed widget cannot crash the page. Fix every error in this report — most are quick wins. Block deploys that introduce new JS errors via CI smoke tests.
How It Works
Headless Chrome subscribes to the runtime exception event, page console events and network failure events during navigation, then reports every error captured with its source URL, line number and stack trace. Third-party errors are grouped by origin so you can see which vendor is causing problems.
Common Mistakes to Avoid
- Shipping new code without monitoring for runtime errors
- Ignoring promise rejections (they show up as unhandledrejection events)
- Allowing third-party script failures to crash the entire page
- Catching errors silently with empty catch blocks
- Treating console errors as "just dev noise"
Quick Checklist
- No uncaught exceptions on page load
- No unhandled promise rejections
- Third-party scripts isolated from first-party crashes
- Error monitor wired up for production
- CI runs a basic JS-error smoke test pre-deploy
Put your whole site on autopilot — SEO and AI search
PositionMySite monitors every signal on this page across your entire website 24/7 — plus keyword rankings, competitor moves and AI-search readiness (llms.txt, schema, ChatGPT & Gemini visibility). When something breaks, you know before Google does.
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Not directly, but pages with broken JavaScript tend to have worse user metrics (bounce, dwell time, INP) which feed page-experience scoring. Fixing errors is hygiene, not SEO theatre.
Add a runtime error monitor (Sentry, Bugsnag) that reports unhandled exceptions and promise rejections from real browsers. This tool catches errors during synthetic page load; production monitoring catches everything else.
Wrap third-party initialisation in try/catch so the third-party failure cannot crash your first-party UX. Report the error to the vendor or remove the script if it is unreliable.
Yes for first-party features. For third-party widget failures, just degrade silently — the user does not need to know your chat widget is broken.
Pre-deploy and post-deploy on every release. Continuously in production via an error monitor. The synthetic test catches load-time issues; production monitoring catches everything else.