Building a Type-Safe API Layer with Next.js and Zod

Type safety shouldn't stop at compile time. With Zod we validate at runtime and infer static types from a single schema.

Why Runtime Validation

TypeScript types vanish at runtime. Zod keeps the contract alive where untrusted data enters your system.

Defining a Schema

const postSchema = z.object({
  title: z.string().min(3),
  slug: z.string().regex(/^[a-z0-9-]+$/),
});

type Post = z.infer<typeof postSchema>;

Using It in a Server Action

export async function createPost(input: unknown) {
  const data = postSchema.parse(input);
  return repository.create(data);
}