Zod schema validation for TypeScript runtime type safety

TypeScript types only exist at compile time. API responses, form inputs, and external data have no runtime type guarantees.

Use Zod for runtime validation that infers TypeScript types: const UserSchema = z.object({ name: z.string(), email: z.string().email() }); type User = z.infer<typeof UserSchema>. Validate at boundaries: UserSchema.parse(apiResponse). Use .safeParse() for error handling. Integrates with: React Hook Form, tRPC, Next.js server actions. Alternatives: Valibot (smaller), Arktype.

TypeScript types are erased at runtime. A type assertion does zero validation. Zod bridges the gap with runtime validation that generates TypeScript types.