TypeScript made it easier to develop big JavaScript applications. Nonetheless at runtime there are no types and thus no data validation. In this session, I motivate why and when we should validate types at runtime and I provide an overview of validation libraries that support us. In particular, I present Zod, TypeBox and class-validator. Finally, I showcase Zod within a React project and how Zod elegantly uses the type system to provide us with lightweight data validation without duplicating code.