Zod

Zod is a TypeScript/JavaScript library for validating data.

In simple terms:

Zod checks whether data has the shape and types you expect.

Example

Suppose your API expects a user:

{
  name: "Reyhaneh",
  age: 25,
  email: "rey@example.com"
}

You can define a Zod schema:

import { z } from "zod";
 
const userSchema = z.object({
  name: z.string(),
  age: z.number(),
  email: z.string().email()
});

Then validate data:

userSchema.parse(user);

If the data is:

{
  name: "Reyhaneh",
  age: "25",
  email: "wrong"
}

Zod rejects it because:

• age should be a number, but it’s a string

• email isn’t a valid email

Where is Zod commonly used?

Especially in frontend + API applications:

Frontend
   ↓
Form data
   ↓
Zod validation
   ↓
API request
   ↓
Backend
   ↓
Zod validation
   ↓
Database

For example, with a login form:

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

This lets you catch invalid input before sending it to the API.

Zod vs TypeScript

A very important distinction:

TypeScript checks types at development/compile time.

type User = {
  name: string;
  age: number;
};

But data coming from an API is runtime data. TypeScript cannot guarantee that the API actually sent what you expect.

Zod can check it at runtime:

TypeScript
   ↓
"According to my code, this should be a User."
 
Zod
   ↓
"Let me check whether the actual data really is a User."

So a common combination is:

TypeScript = type safety during development
Zod = runtime validation of actual data

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