Next.js: How to validate forms on the server
15 June 2025 (Updated 15 June 2025)
Write your validation logic inside your server function:
'use server'
import { z } from 'zod'
const schema = z.object({
email: z.string({
invalid_type_error: 'Invalid Email',
}),
})
export default async function createUser(formData: FormData) {
const validatedFields = schema.safeParse({
email: formData.get('email'),
})
// Return early if the form data is invalid
if (!validatedFields.success) {
return {
errors: validatedFields.error.flatten().fieldErrors,
}
}
// Mutate data
}
Display the validation errors on the client-side. You’ll need to convert your components that uses <form>
to be a Client Component and then use React’s useActionState hook.
'use client'
import { useActionState } from 'react'
import { createUser } from '@/app/actions'
const initialState = {
message: '',
}
export function Signup() {
const [state, formAction, pending] = useActionState(createUser, initialState)
return (
<form action={formAction}>
<label htmlFor="email">Email</label>
<input type="text" id="email" name="email" required />
{/* ... */}
<p aria-live="polite">{state?.message}</p>
<button disabled={pending}>Sign up</button>
</form>
)
}
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Next.js recipes