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schemas-7lnl63oDefining Schemas

Last Updated: 3/12/2026

Defining Schemas

Zod provides schema constructors for all JavaScript primitives and common data structures. This guide covers the most frequently used schema types.

Primitives

import * as z from "zod";
 
z.string();    // string
z.number();    // number
z.boolean();   // boolean
z.bigint();    // bigint
z.date();      // Date
z.null();      // null
z.undefined(); // undefined

Strings

String schemas support validation methods for common patterns:

const Username = z.string()
  .min(3, "Username must be at least 3 characters")
  .max(20, "Username cannot exceed 20 characters")
  .regex(/^[a-zA-Z0-9_]+$/, "Only letters, numbers, and underscores allowed");
 
const Email = z.string().email("Invalid email address");
const URL = z.string().url("Invalid URL");

Numbers

Number schemas provide range and format validation:

const Age = z.number()
  .int("Age must be an integer")
  .positive("Age must be positive")
  .max(120, "Age cannot exceed 120");
 
const Price = z.number()
  .nonnegative("Price cannot be negative")
  .multipleOf(0.01, "Price must have at most 2 decimal places");

Objects

Object schemas define the shape of an object:

const User = z.object({
  id: z.number(),
  username: z.string(),
  email: z.string().email(),
  age: z.number().int().positive().optional(),
});
 
// Type: { id: number; username: string; email: string; age?: number | undefined }

By default, Zod objects are strict — they reject unknown keys:

User.parse({
  id: 1,
  username: "billie",
  email: "billie@example.com",
  extra: "field", // ✗ throws error
});

To allow unknown keys, use .passthrough() or create a loose object:

const LooseUser = User.passthrough();
// or
const LooseUser = z.looseObject({ /* shape */ });

Arrays

Array schemas validate each element:

const Tags = z.array(z.string())
  .min(1, "At least one tag required")
  .max(5, "Maximum 5 tags allowed");
 
// Type: string[]

What’s Next

Type InferenceUnions