When no route matches the URL, or a page throws while rendering, kit renders the root error.ts instead of the page. It receives the error and the current location:

export default function ErrorPage({ error, url }) {
	error.code; // 404 for unmatched paths, 500 for render errors
	error.message;
}

error.ts lives directly in src/routes and only there — one error page per app.

Your task

1. In src/routes/error.ts, render error.code and error.message instead of the generic text.

You're done when the two failure modes look different: typing a nonsense path like /nope into the URL bar shows 404 with "Not Found", and visiting /broken (its page throws on render) shows 500 with the thrown message.