Zod 4 Schema Validation - Patterns & Breaking Changes

---

name: zod-4 description: > Zod 4 schema validation patterns. Trigger: When using Zod for validation - breaking changes from v3. license: Apache-2.0 metadata: version: '1.0'

Breaking Changes from Zod 3

// ❌ Zod 3 (OLD)
z.string().email();
z.string().uuid();
z.string().url();
z.string().nonempty();
z.object({ name: z.string() }).required_error('Required');

// ✅ Zod 4 (NEW)
z.email();
z.uuid();
z.url();
z.string().min(1);
z.object({ name: z.string() }, { error: 'Required' });

Basic Schemas

import { z } from 'zod';

// Primitives
const stringSchema = z.string();
const numberSchema = z.number();
const booleanSchema = z.boolean();
const dateSchema = z.date();

// Top-level validators (Zod 4)
const emailSchema = z.email();
const uuidSchema = z.uuid();
const urlSchema = z.url();

// With constraints
const nameSchema = z.string().min(1).max(100);
const ageSchema = z.number().int().positive().max(150);
const priceSchema = z.number().min(0).multipleOf(0.01);

Object Schemas

const userSchema = z.object({
  id: z.uuid(),
  email: z.email({ error: 'Invalid email address' }),
  name: z.string().min(1, { error: 'Name is required' }),
  age: z.number().int().positive().optional(),
  role: z.enum(['admin', 'user', 'guest']),
  metadata: z.record(z.string(), z.unknown()).optional()
});

type User = z.infer<typeof userSchema>;

// Parsing
const user = userSchema.parse(data); // Throws on error
const result = userSchema.safeParse(data); // Returns { success, data/error }

if (result.success) {
  console.log(result.data);
} else {
  console.log(result.error.issues);
}

Arrays and Records

// Arrays
const tagsSchema = z.array(z.string()).min(1).max(10);
const numbersSchema = z.array(z.number()).nonempty();

// Records (objects with dynamic keys)
const scoresSchema = z.record(z.string(), z.number());
// { [key: string]: number }

// Tuples
const coordinatesSchema = z.tuple([z.number(), z.number()]);
// [number, number]

Unions and Discriminated Unions

// Simple union
const stringOrNumber = z.union([z.string(), z.number()]);

// Discriminated union (more efficient)
const resultSchema = z.discriminatedUnion('status', [
  z.object({ status: z.literal('success'), data: z.unknown() }),
  z.object({ status: z.literal('error'), error: z.string() })
]);

Transformations

// Transform during parsing
const lowercaseEmail = z.email().transform(email => email.toLowerCase());

// Coercion (convert types)
const numberFromString = z.coerce.number(); // "42" → 42
const dateFromString = z.coerce.date(); // "2024-01-01" → Date

// Preprocessing
const trimmedString = z.preprocess(
  val => (typeof val === 'string' ? val.trim() : val),
  z.string()
);

Refinements

const passwordSchema = z
  .string()
  .min(8)
  .refine(val => /[A-Z]/.test(val), {
    message: 'Must contain uppercase letter'
  })
  .refine(val => /[0-9]/.test(val), {
    message: 'Must contain number'
  });

// With superRefine for multiple errors
const formSchema = z
  .object({
    password: z.string(),
    confirmPassword: z.string()
  })
  .superRefine((data, ctx) => {
    if (data.password !== data.confirmPassword) {
      ctx.addIssue({
        code: z.ZodIssueCode.custom,
        message: "Passwords don't match",
        path: ['confirmPassword']
      });
    }
  });

Optional and Nullable

// Optional (T | undefined)
z.string().optional();

// Nullable (T | null)
z.string().nullable();

// Both (T | null | undefined)
z.string().nullish();

// Default values
z.string().default('unknown');
z.number().default(() => Math.random());

Error Handling

// Zod 4: Use 'error' param instead of 'message'
const schema = z.object({
  name: z.string({ error: 'Name must be a string' }),
  email: z.email({ error: 'Invalid email format' }),
  age: z.number().min(18, { error: 'Must be 18 or older' })
});

// Custom error map
const customSchema = z.string({
  error: issue => {
    if (issue.code === 'too_small') {
      return 'String is too short';
    }
    return 'Invalid string';
  }
});

React Hook Form Integration

import { useForm } from "react-hook-form";
import { zodResolver } from "@hookform/resolvers/zod";

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

type FormData = z.infer<typeof schema>;

function Form() {
  const { register, handleSubmit, formState: { errors } } = useForm<FormData>({
    resolver: zodResolver(schema),
  });

  return (
    <form onSubmit={handleSubmit(onSubmit)}>
      <input {...register("email")} />
      {errors.email && <span>{errors.email.message}</span>}
    </form>
  );
}

Keywords

zod, validation, schema, typescript, forms, parsing