sveltejs/kit · warning

The form action returned a value, but it isn't available in

Error message

The form action returned a value, but it isn't available in `page.form`, because SSR is off. To handle the returned value in CSR, enhance your form with `use:enhance`. See https://svelte.dev/docs/kit/form-actions#progressive-enhancement-use-enhance

What it means

When SSR is disabled (`ssr = false` or `export const ssr = false`), the server renders no HTML, so a value returned by a form action cannot be placed into `page.form` in the initial response. SvelteKit warns that the action's return value is being lost and recommends using `use:enhance` so the result is delivered via the client-side fetch instead.

Source

Thrown at packages/kit/src/runtime/server/page/index.js:127

		const csr = nodes.csr();

		// renders an empty 'shell' page if SSR is turned off and if there is
		// no server data to prerender. As a result, the load functions and rendering
		// only occur client-side.
		if (
			ssr === false &&
			!((state.prerendering || state.prerender_default === true) && should_prerender_data)
		) {
			// if the user makes a request through a non-enhanced form, the returned value is lost
			// because there is no SSR or client-side handling of the response
			if (DEV && action_result && !event.request.headers.has('x-sveltekit-action')) {
				if (action_result.type === 'error') {
					console.warn(
						"The form action returned an error, but +error.svelte wasn't rendered because SSR is off. To get the error page with CSR, enhance your form with `use:enhance`. See https://svelte.dev/docs/kit/form-actions#progressive-enhancement-use-enhance"
					);
				} else if (action_result.data) {
					/// case: lost data
					console.warn(
						"The form action returned a value, but it isn't available in `page.form`, because SSR is off. To handle the returned value in CSR, enhance your form with `use:enhance`. See https://svelte.dev/docs/kit/form-actions#progressive-enhancement-use-enhance"
					);
				}
			}

			return await render_response({
				// provide nodes without running load functions so that the styles and
				// fonts are linked in the head before CSR takes over
				branch: compact(nodes.data).map((node) => {
					return {
						node,
						data: null,
						server_data: null
					};
				}),
				fetched,
				page_config: {
					ssr: false,

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Enhance the form with `use:enhance` from `$app/forms` so the action result reaches the client.
2. Enable SSR for the page (`export const ssr = true` or remove the override) so `page.form` is hydrated server-side.
3. Redesign the action to redirect on success instead of returning data if you must keep SSR off and no enhance.

Example fix

<!-- before -->
<form method="POST" action="?/create">...</form>
<!-- after -->
<script>
  import { enhance } from '$app/forms';
</script>
<form method="POST" action="?/create" use:enhance>...</form>

// client-side check before relying on page.form
if (!ssrEnabledForThisRoute && !formIsEnhanced) {
  console.warn('action return value will be lost; use use:enhance or enable SSR');
}

When it happens

Trigger: A `<form method="POST">` posts to an action on a page with SSR off, the action returns `{ success: true, ... }` (non-error data), and the form is NOT enhanced with `use:enhance`; render_page detects `action_result.data` but cannot serialize it into the CSR-only render.

Common situations: Progressive-enhancement pages exported with `export const ssr = false` where developers expect `page.form` to be populated after a plain (non-JS-enhanced) form submission.

Related errors

• Cannot `return redirect(...)` — use `redirect(...)` instead
• Cannot `return error(...)` — use `error(...)` or `return fai
• Data returned from action inside ${route_id} is not serializ
• Data returned from action inside ${route_id} is not serializ
• Cannot prerender pages with actions

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/562273316f0d4e6f. Report an issue: GitHub.