Zod
Zod is a TypeScript-first schema declaration and validation library that lets developers define a schema once and use it for both runtime validation and static type inference.
Definition
Zod is a TypeScript-first schema declaration and validation library that lets developers define a schema once and use it for both runtime validation and static type inference.
Overview
Zod addresses the gap between TypeScript's compile-time-only type system and the need to validate data at runtime — API responses, form input, environment variables — where TypeScript's types offer no actual protection once code is compiled. Developers declare a schema using Zod's chainable API (z.object, z.string, z.number, and so on), which can validate arbitrary input and, on success, infer a precise TypeScript type via z.infer. This eliminates duplicate type and validation definitions that would otherwise drift out of sync. Zod also supports transformations, refinements, unions, and detailed, structured error reporting when validation fails. Zod is commonly used in React and Next.js applications for form validation, often paired with react-hook-form, and for validating API request and response bodies. It's increasingly used as the schema layer for typed ORMs and RPC-style APIs alongside tools like Drizzle ORM or Prisma, and it's a natural companion to the concepts covered in a TypeScript course.
Key Features
- Chainable schema API covering primitives, objects, arrays, and unions
- Static type inference from schemas via z.infer, avoiding duplicate types
- Built-in data transformations and custom refinements
- Detailed, structured validation error reporting
- Composable schemas for nested and recursive data structures
- Zero dependencies and a small bundle size