sveltejs/kit · error

Your form contains <input type="file"> fields, but is missin

Error message

Your form contains <input type="file"> fields, but is missing the necessary `enctype="multipart/form-data"` attribute. This will lead to inconsistent behavior between enhanced and native forms. For more details, see https://github.com/sveltejs/kit/issues/9819.

What it means

When a remote form's enctype is not multipart/form-data but the submitted FormData contains File values, enhanced and native submissions would behave inconsistently (native forms would silently drop or mis-encode files). SvelteKit throws in validate_form_data to surface this mismatch early.

Source

Thrown at packages/kit/src/runtime/client/remote-functions/form.svelte.js:841

}

/**
 * @param {FormData} form_data
 * @param {string} enctype
 */
function validate_form_data(form_data, enctype) {
	for (const key of form_data.keys()) {
		if (/^\$[.[]?/.test(key)) {
			throw new Error(
				'`$` is used to collect all FormData validation issues and cannot be used as the `name` of a form control'
			);
		}
	}

	if (enctype !== 'multipart/form-data') {
		for (const value of form_data.values()) {
			if (value instanceof File) {
				throw new Error(
					'Your form contains <input type="file"> fields, but is missing the necessary `enctype="multipart/form-data"` attribute. This will lead to inconsistent behavior between enhanced and native forms. For more details, see https://github.com/sveltejs/kit/issues/9819.'
				);
			}
		}
	}
}

View on GitHub (pinned to 03f1687fe6)

Solutions

1. Add enctype="multipart/form-data" to the <form> element
2. Remove the file input if file upload is not intended
3. Handle the file via a separate upload endpoint/form with the correct enctype

Example fix

// before
<form method="POST" use:enhance>
  <input type="file" name="doc" />
</form>
// after
<form method="POST" enctype="multipart/form-data" use:enhance>
  <input type="file" name="doc" />
</form>

function needsMultipart(form) {
  return form.enctype !== 'multipart/form-data' &&
    form.querySelectorAll('input[type="file"]').length > 0;
}
// if true, set enctype before submit

When it happens

Trigger: Adding <input type="file"> to a <form> whose enctype remains the default application/x-www-form-urlencoded (or is unset), then submitting the enhanced remote form.

Common situations: Retrofitting a file upload into an existing text-only form without updating enctype; forgetting enctype on forms that grew file inputs over time; see sveltejs/kit#9819.

Related errors

• Can only use the `multiple` attribute when `name` includes a
• Cannot mix and match file and non-file inputs under the same
• `$` is used to collect all FormData validation issues and ca
• Your form contains <input type="file"> fields, but is missin
• Cannot call submit() before the form is attached

AI-assisted analysis of sveltejs/kit@03f1687fe6 (2026-09-02). Data as JSON: /api/errors/f85763cf1c8dcb6f. Report an issue: GitHub.