Zod

ELI5 — The Vibe Check

Zod is a TypeScript library for validating data at runtime. TypeScript types disappear when your code runs — they only exist at compile time. Zod bridges that gap: you define a schema, and Zod checks actual data against it at runtime AND gives you the TypeScript type for free. One schema, two jobs. It's the 'trust but verify' of TypeScript.

Real Talk

Zod is a TypeScript-first schema declaration and validation library with zero dependencies. It provides runtime validation with automatic TypeScript type inference — define a schema once and get both runtime validation and static types. Zod schemas are composable, immutable, and support complex types (unions, intersections, transforms, refinements). It's the de facto standard for form validation (React Hook Form), API input validation (tRPC, Express), and environment variable parsing.

Show Me The Code

import { z } from 'zod';

const UserSchema = z.object({
  name: z.string().min(2),
  email: z.string().email(),
  age: z.number().int().positive().optional(),
});

// TypeScript type inferred automatically
type User = z.infer<typeof UserSchema>;
// { name: string; email: string; age?: number }

const result = UserSchema.safeParse(formData);
if (!result.success) {
  console.log(result.error.issues);
}

When You'll Hear This

"Validate the API input with Zod — never trust client data." / "Zod infers the TypeScript type from the schema — no duplication."