Type-Safe API Validation with TypeScript and Zod

Types alone do not validate requests

TypeScript disappears at runtime. A request coming from a browser, mobile client, or third-party integration can still contain missing fields, incorrect types, or unexpected values. Runtime validation closes that gap.

Define one schema at the boundary

A Zod schema can describe the expected payload and produce a typed result after parsing. Keep the schema close to the API contract, validate before business logic runs, and return a consistent error shape to the client.

const CreateUser = z.object({
  name: z.string().min(2),
  email: z.string().email(),
});

const input = CreateUser.parse(requestBody);

Validate more than the body

Path parameters, query strings, headers, uploaded files, and environment variables are all external input. Applying the same discipline to every boundary prevents many production-only bugs.

Keep error messages useful

Do not expose stack traces or internal implementation details. Return field-level messages that help a user correct their input while logging the full diagnostic context on the server.