Is your page throwing JavaScript errors?
Paste your page and we load it in a real browser, then surface the JavaScript console errors and failed requests firing under the hood while the page looks fine. Free, no signup.
What we check
We load the page you submit in a real browser, the way a visitor's browser runs it, and watch for two things: JavaScript errors logged to the console, and network requests that fail to load (a script, an image, an API call that errors out). When either happens, we surface what we caught so you can see it.
This tells you that something is erroring, not why - we're not a debugger, and we don't trace it to a line of code. We also can't grade severity for you: a failed request might be a harmless missing favicon or a dead checkout API, so we show you what fired and let you judge which it is. What it does catch is the gap between 'the page looks fine' and 'the page is quietly broken underneath.'
Why it matters
JavaScript fails silently. A script throws on load, an API call 404s, a third-party widget errors out - and the page still mostly renders, so nothing looks wrong from the outside. The break is in the console, which you only open when you already suspect something. Most visitors never tell you; they just hit the thing that doesn't work and leave.
This is the classic 'works on my machine' trap. It loaded fine when you built it, then a dependency changed, an env var went missing in production, or a script started 404ing - and now it's throwing for real users while looking perfect to you. Catching the errors that fire on load means you find out before a customer hits the broken part.
Questions
What do you actually catch?
JavaScript errors written to the browser console on load, and network requests that failed (a script, image, or API call that errored). We render the page in a real browser and surface what fired, so you can see what's breaking under the hood.
Do you tell me how to fix the error?
No. We surface the errors firing on your page so you know they exist; we're not a debugger and don't trace them to a line of code. Think of it as the alarm, not the diagnosis - it tells you where to start looking.
Is a single failed request always a problem?
Not necessarily. A failed request can be a harmless missing favicon or a genuinely dead API call, and they look similar from the outside. We show you what fired rather than guess at severity, so you can tell the noise from the real break.
Is it really free?
Yes. Paste a URL and run it, no account needed. The same scan also runs all of CopyMosaic's other checks, and you can open the full report to see them.