Mastering JSON Validation with Zod: From Type Safety to Runtime Safety

What is Zod?

Zod is a TypeScript-first schema declaration and validation library. It allows you to dynamically check if data returned from an API matches your expectations while simultaneously extracting TypeScript types, ensuring both runtime reliability and type safety.

Why Do We Need Runtime Validation?

TypeScript’s type checking only happens at compile time. Once your code is running in the browser, it has no way of knowing if the data returned by an API has changed or contains unexpected null values. Zod fills this gap.

Basic Usage

Define a schema and parse your data:

import { z } from "zod";

const UserSchema = z.object({
  id: z.number(),
  username: z.string(),
  email: z.string().email(),
});

// Extract types automatically
type User = z.infer<typeof UserSchema>;

// Validate data
const result = UserSchema.safeParse(apiData);
if (result.success) {
  const user = result.data; // Fully typed
} else {
  console.error(result.error);
}

Key Features of Zod

• Zero Dependencies: Lightweight and efficient.
• Developer Friendly: Great error messages and intuitive API.
• Coercion: Can convert strings to numbers or dates during validation.
• Transformation: Clean up or modify data as it passes through the schema.

Conclusion

Manually creating Zod schemas from large JSON structures can be tedious. Using a “JSON to Zod” converter can jumpstart your development, providing a solid foundation for robust data validation in your TypeScript projects.