React form validator

React Form Validator

Auto-enforces React Hook Form + Zod validation pattern for ALL forms in Next.js/React applications.

Activation Triggers

This skill activates when:

• Creating form components
• Using <form>, <input>, form elements
• Mentioning "form", "validation", "submit", "input"
• Handling form state or submission
• Creating login, signup, or data entry forms

Required Form Pattern (MANDATORY)

ALL forms MUST use:

• ✅ React Hook Form for form state management
• ✅ Zod for schema validation
• ✅ TypeScript types inferred from Zod schema
• ✅ Error handling with accessible error messages
• ✅ Loading states during submission

Auto-Validation Process

Step 1: Detect Form Without Pattern

When detecting a form being created:

// ❌ WRONG - Uncontrolled form, no validation
function LoginForm() {
  const handleSubmit = (e) => {
    e.preventDefault()
    const email = e.target.email.value  // No validation!
    const password = e.target.password.value
    // Submit...
  }

  return (
    <form onSubmit={handleSubmit}>
      <input name="email" type="email" />
      <input name="password" type="password" />
      <button>Login</button>
    </form>
  )
}

Step 2: Identify Missing Requirements

Detect:

• ❌ No React Hook Form
• ❌ No Zod validation
• ❌ No TypeScript types
• ❌ No error display
• ❌ No loading state

Step 3: Auto-Fix to Correct Pattern

After (Correct Pattern):

'use client'
import { useForm } from 'react-hook-form'
import { zodResolver } from '@hookform/resolvers/zod'
import * as z from 'zod'

// 1. Define Zod schema
const loginSchema = z.object({
  email: z.string().email('Invalid email address'),
  password: z.string().min(8, 'Password must be at least 8 characters'),
})

// 2. Infer TypeScript type from schema
type LoginFormData = z.infer<typeof loginSchema>

function LoginForm() {
  // 3. Set up React Hook Form with Zod resolver
  const {
    register,
    handleSubmit,
    formState: { errors, isSubmitting },
  } = useForm<LoginFormData>({
    resolver: zodResolver(loginSchema),
  })

  // 4. Type-safe submit handler
  const onSubmit = async (data: LoginFormData) => {
    try {
      await loginUser(data)
      // Handle success
    } catch (error) {
      // Handle error
    }
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-4">
      {/* Email field */}
      <div>
        <label htmlFor="email" className="block text-sm font-medium">
          Email
        </label>
        <input
          {...register('email')}
          id="email"
          type="email"
          className="mt-1 block w-full rounded-md border-gray-300"
          aria-invalid={!!errors.email}
          aria-describedby={errors.email ? 'email-error' : undefined}
        />
        {errors.email && (
          <p id="email-error" className="mt-1 text-sm text-red-600" role="alert">
            {errors.email.message}
          </p>
        )}
      </div>

      {/* Password field */}
      <div>
        <label htmlFor="password" className="block text-sm font-medium">
          Password
        </label>
        <input
          {...register('password')}
          id="password"
          type="password"
          className="mt-1 block w-full rounded-md border-gray-300"
          aria-invalid={!!errors.password}
          aria-describedby={errors.password ? 'password-error' : undefined}
        />
        {errors.password && (
          <p id="password-error" className="mt-1 text-sm text-red-600" role="alert">
            {errors.password.message}
          </p>
        )}
      </div>

      {/* Submit button with loading state */}
      <button
        type="submit"
        disabled={isSubmitting}
        className="w-full py-2 px-4 bg-blue-600 text-white rounded hover:bg-blue-700 disabled:opacity-50"
      >
        {isSubmitting ? 'Logging in...' : 'Login'}
      </button>
    </form>
  )
}

Step 4: Explain Pattern

Form Pattern Applied

Added:

1. ✅ Zod schema for validation
2. ✅ TypeScript types inferred from schema
3. ✅ React Hook Form for state management
4. ✅ zodResolver connects Zod to React Hook Form
5. ✅ Error messages displayed accessibly
6. ✅ Loading state during submission

Why:

• Zod provides runtime type validation
• React Hook Form handles form state efficiently
• Type safety prevents bugs
• Accessible error messages help all users

Complete Form Patterns

Pattern 1: Simple Contact Form

import { useForm } from 'react-hook-form'
import { zodResolver } from '@hookform/resolvers/zod'
import * as z from 'zod'

const contactSchema = z.object({
  name: z.string().min(2, 'Name must be at least 2 characters'),
  email: z.string().email('Invalid email address'),
  message: z.string().min(10, 'Message must be at least 10 characters'),
})

type ContactFormData = z.infer<typeof contactSchema>

export function ContactForm() {
  const {
    register,
    handleSubmit,
    reset,
    formState: { errors, isSubmitting, isSubmitSuccessful },
  } = useForm<ContactFormData>({
    resolver: zodResolver(contactSchema),
  })

  const onSubmit = async (data: ContactFormData) => {
    await sendContactMessage(data)
    reset() // Clear form after success
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-4">
      <div>
        <label htmlFor="name">Name</label>
        <input {...register('name')} id="name" type="text" />
        {errors.name && <p role="alert">{errors.name.message}</p>}
      </div>

      <div>
        <label htmlFor="email">Email</label>
        <input {...register('email')} id="email" type="email" />
        {errors.email && <p role="alert">{errors.email.message}</p>}
      </div>

      <div>
        <label htmlFor="message">Message</label>
        <textarea {...register('message')} id="message" rows={4} />
        {errors.message && <p role="alert">{errors.message.message}</p>}
      </div>

      <button type="submit" disabled={isSubmitting}>
        {isSubmitting ? 'Sending...' : 'Send Message'}
      </button>

      {isSubmitSuccessful && (
        <p className="text-green-600">Message sent successfully!</p>
      )}
    </form>
  )
}

Pattern 2: Complex Registration Form

const registerSchema = z.object({
  email: z.string().email(),
  password: z.string().min(8).regex(/[A-Z]/, 'Must contain uppercase letter'),
  confirmPassword: z.string(),
  firstName: z.string().min(2),
  lastName: z.string().min(2),
  terms: z.boolean().refine((val) => val === true, {
    message: 'You must accept the terms and conditions',
  }),
}).refine((data) => data.password === data.confirmPassword, {
  message: "Passwords don't match",
  path: ['confirmPassword'],
})

type RegisterFormData = z.infer<typeof registerSchema>

export function RegisterForm() {
  const {
    register,
    handleSubmit,
    formState: { errors, isSubmitting },
  } = useForm<RegisterFormData>({
    resolver: zodResolver(registerSchema),
  })

  const onSubmit = async (data: RegisterFormData) => {
    await createUser(data)
  }

  return (
    <form onSubmit={handleSubmit(onSubmit)} className="space-y-4">
      {/* Email */}
      <div>
        <label htmlFor="email">Email</label>
        <input {...register('email')} id="email" type="email" />
        {errors.email && <p role="alert">{errors.email.message}</p>}
      </div>

      {/* Password */}
      <div>
        <label htmlFor="password">Password</label>
        <input {...register('password')} id="password" type="password" />
        {errors.password && <p role="alert">{errors.password.message}</p>}
      </div>

      {/* Confirm Password */}
      <div>
        <label htmlFor="confirmPassword">Confirm Password</label>
        <input {...register('confirmPassword')} id="confirmPassword" type="password" />
        {errors.confirmPassword && <p role="alert">{errors.confirmPassword.message}</p>}
      </div>

      {/* First Name */}
      <div>
        <label htmlFor="firstName">First Name</label>
        <input {...register('firstName')} id="firstName" type="text" />
        {errors.firstName && <p role="alert">{errors.firstName.message}</p>}
      </div>

      {/* Last Name */}
      <div>
        <label htmlFor="lastName">Last Name</label>
        <input {...register('lastName')} id="lastName" type="text" />
        {errors.lastName && <p role="alert">{errors.lastName.message}</p>}
      </div>

      {/* Terms checkbox */}
      <div>
        <label className="flex items-center">
          <input {...register('terms')} type="checkbox" className="mr-2" />
          I accept the terms and conditions
        </label>
        {errors.terms && <p role="alert">{errors.terms.message}</p>}
      </div>

      <button type="submit" disabled={isSubmitting}>
        {isSubmitting ? 'Creating account...' : 'Sign Up'}
      </button>
    </form>
  )
}

Pattern 3: Multi-Step Form

const step1Schema = z.object({
  email: z.string().email(),
  password: z.string().min(8),
})

const step2Schema = z.object({
  firstName: z.string().min(2),
  lastName: z.string().min(2),
  phone: z.string().optional(),
})

type Step1Data = z.infer<typeof step1Schema>
type Step2Data = z.infer<typeof step2Schema>

export function MultiStepForm() {
  const [step, setStep] = useState(1)
  const [formData, setFormData] = useState<Partial<Step1Data & Step2Data>>({})

  const step1Form = useForm<Step1Data>({
    resolver: zodResolver(step1Schema),
  })

  const step2Form = useForm<Step2Data>({
    resolver: zodResolver(step2Schema),
  })

  const handleStep1 = (data: Step1Data) => {
    setFormData({ ...formData, ...data })
    setStep(2)
  }

  const handleStep2 = async (data: Step2Data) => {
    const finalData = { ...formData, ...data }
    await submitRegistration(finalData)
  }

  return (
    <div>
      {step === 1 && (
        <form onSubmit={step1Form.handleSubmit(handleStep1)}>
          {/* Step 1 fields */}
          <button type="submit">Next</button>
        </form>
      )}

      {step === 2 && (
        <form onSubmit={step2Form.handleSubmit(handleStep2)}>
          {/* Step 2 fields */}
          <button type="button" onClick={() => setStep(1)}>
            Back
          </button>
          <button type="submit">Submit</button>
        </form>
      )}
    </div>
  )
}

Advanced Zod Patterns

Custom Validation

const userSchema = z.object({
  username: z.string()
    .min(3)
    .max(20)
    .regex(/^[a-zA-Z0-9_]+$/, 'Only letters, numbers, and underscores allowed'),
  age: z.number()
    .int()
    .min(18, 'Must be 18 or older')
    .max(120),
  website: z.string().url().optional(),
})

Async Validation

const emailSchema = z.string().email().refine(
  async (email) => {
    const available = await checkEmailAvailability(email)
    return available
  },
  { message: 'Email already in use' }
)

Conditional Fields

const shippingSchema = z.object({
  sameAsBilling: z.boolean(),
  address: z.string().optional(),
  city: z.string().optional(),
  zip: z.string().optional(),
}).refine(
  (data) => {
    if (!data.sameAsBilling) {
      return !!data.address && !!data.city && !!data.zip
    }
    return true
  },
  {
    message: 'Shipping address is required',
    path: ['address'],
  }
)

Form Component Reusability

// Reusable FormField component
interface FormFieldProps {
  label: string
  name: string
  type?: string
  register: UseFormRegister<any>
  error?: FieldError
  required?: boolean
}

function FormField({ label, name, type = 'text', register, error, required }: FormFieldProps) {
  const id = `field-${name}`

  return (
    <div>
      <label htmlFor={id} className="block text-sm font-medium">
        {label} {required && <span className="text-red-600">*</span>}
      </label>
      <input
        {...register(name)}
        id={id}
        type={type}
        className="mt-1 block w-full rounded-md border-gray-300"
        aria-invalid={!!error}
        aria-describedby={error ? `${id}-error` : undefined}
        aria-required={required}
      />
      {error && (
        <p id={`${id}-error`} className="mt-1 text-sm text-red-600" role="alert">
          {error.message}
        </p>
      )}
    </div>
  )
}

// Usage
function LoginForm() {
  const { register, handleSubmit, formState: { errors } } = useForm<LoginFormData>({
    resolver: zodResolver(loginSchema),
  })

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <FormField
        label="Email"
        name="email"
        type="email"
        register={register}
        error={errors.email}
        required
      />
      <FormField
        label="Password"
        name="password"
        type="password"
        register={register}
        error={errors.password}
        required
      />
      <button type="submit">Login</button>
    </form>
  )
}

Server Actions Integration (Next.js 14+)

'use server'
import { z } from 'zod'

const contactSchema = z.object({
  name: z.string().min(2),
  email: z.string().email(),
  message: z.string().min(10),
})

export async function submitContact(formData: FormData) {
  const data = {
    name: formData.get('name'),
    email: formData.get('email'),
    message: formData.get('message'),
  }

  const result = contactSchema.safeParse(data)

  if (!result.success) {
    return { success: false, errors: result.error.flatten() }
  }

  // Process valid data
  await saveContact(result.data)
  return { success: true }
}

Success Criteria

✅ ALL forms use React Hook Form ✅ ALL forms use Zod validation ✅ TypeScript types inferred from schemas ✅ Error messages displayed accessibly ✅ Loading states during submission ✅ Forms are keyboard accessible ✅ ARIA attributes for errors

Behavior

Proactive enforcement:

• Detect forms without being asked
• Add React Hook Form + Zod automatically
• Generate complete form code
• Explain benefits of the pattern
• Ensure accessibility

Never:

• Allow unvalidated forms
• Accept useState for form state
• Allow inline validation logic
• Skip TypeScript types

Block completion if:

• Form lacks validation
• No error handling
• Missing loading states
• Not using React Hook Form + Zod

This ensures all forms are type-safe, validated, and accessible from day one.