When a validation failure causes a redirect loop

Laravel's default behavior on a failed FormRequest validation is to throw a ValidationException, which the framework's exception handler converts into a redirect to the previous URL with the input flashed to the session and errors attached.

That works perfectly when the form was opened from a referring page in the same app. It breaks down when there is no previous URL, for example a bookmark to a GET form with validation, or submitting something into a target="_blank" (like PDF generation).

In all of these, Laravel tries to redirect to url()->previous(). With no previous url, "previous" resolves to the form itself. The form submits, validation fails, the framework redirects to the form, the form auto-submits again and the user is stuck.

One fix for this rare condition is to override failedValidation() on the FormRequest and abort with a 422 instead of letting the default redirect behavior run:

protected function failedValidation(Validator $validator): void
{
    abort(422, sprintf(
        'A validation error occurred: %s',
        $validator->errors()->first()
    ));
}

This may not be the most elegant solution, but it stops the loop. Validation failures on these routes tend to be rare in practice, so showing the first error is enough information.

You could also override getRedirectUrl() instead of failedValidation(), which lets you keep Laravel's normal flash-and-redirect flow. But then you need to have a location to redirect them to, and also a way to show error messages. I don't think that's worth it if this is a non-standard user flow and the result of good defense in depth coding.

Here to help,

Aaron

P.S. Edge cases like this are a big reason we wrote a whole book on Laravel validation. It walks through every built-in rule with real examples.