Attempted to preload a URL that does not belong to this app:

Error message

Attempted to preload a URL that does not belong to this app: ${url}

What it means

preloadData() resolves the href against the app's route table via get_navigation_intent(); if no route matches, the URL does not belong to the app and preloading cannot proceed, so it throws. Preloading is an optimization for in-app navigations only.

Source

Thrown at packages/kit/src/runtime/client/client.js:2801

/**
 * Programmatically preloads the given page, which means
 *  1. ensuring that the code for the page is loaded, and
 *  2. calling the page's load function with the appropriate options.
 *
 * This is the same behaviour that SvelteKit triggers when the user taps or mouses over an `<a>` element with `data-sveltekit-preload-data`.
 * If the next navigation is to `href`, the values returned from load will be used, making navigation instantaneous.
 * Returns a Promise that resolves with the result of running the new route's `load` functions once the preload is complete.
 *
 * @param {string} href Page to preload
 * @returns {Promise<({ type: 'loaded'; data: Record<string, any> } | { type: 'redirect'; location: string } | { type: 'error'; error: App.Error }) & { status: number; }>}
 */
export async function preloadData(href) {
	const url = resolve_url(href);
	const intent = await get_navigation_intent(url, false);

	if (!intent) {
		throw new Error(`Attempted to preload a URL that does not belong to this app: ${url}`);
	}

	/** @type {Awaited<ReturnType<typeof _preload_data>>} */
	let result;

	try {
		result = await _preload_data(intent);
	} catch (error) {
		// `load_route` throws the handled error (an `App.Error` with a `status`)
		// when a preload fails, so surface it in the documented `{ type: 'error' }` shape
		const handled = /** @type {App.Error & { status?: number }} */ (error);
		return {
			type: 'error',
			status: handled?.status ?? 500,
			error: handled
		};
	}

View on GitHub (pinned to 03f1687fe6)

Solutions

Only call preloadData for same-origin hrefs that match a route
Guard with a try/catch or route check before preloading
Filter external links out of your prefetch logic (check url.origin)

Example fix

// before
link.addEventListener('mouseenter', () => preloadData(link.href));
// after
link.addEventListener('mouseenter', () => {
  const u = new URL(link.href, location.href);
  if (u.origin === location.origin) preloadData(u.pathname).catch(() => {});
});

Defensive patterns

Strategy: try-catch

Validate before calling

function canPreload(href) {
  const u = new URL(href, location.href);
  return u.origin === location.origin && !u.pathname.startsWith('/api/');
}

Try / catch

try { await preloadData(href); } catch { /* not an app route; skip */ }

Prevention

Filter external links before prefetching on hover/viewport
Only preload hrefs generated from your own route table
Treat preload failures as non-fatal optimizations

When it happens

Trigger: preloadData('https://cdn.example.com/x.js') or preloadData('/path-without-route'); calling it from an <a> hover handler for external links; stale hrefs after route removal.

Common situations: Custom link-hover prefetch utilities that don't filter external/route-less URLs; dynamic URLs built from CMS content pointing outside the app.

Related errors

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/25063532968dd357. Report an issue: GitHub.