How to Validate API Requests with Zod in Node.js (2026 Guide)

Every API you build has one thing in common: it accepts input from the outside world. And the outside world cannot be trusted . Whether it's a malformed JSON body, a missing required field, or an age field set to "banana" , bad input is the #1 source of bugs, crashes, and security vulnerabilities in backend applications. In this guide, you'll learn how to use Zod — the TypeScript-first schema validation library — to validate every API request before it reaches your business logic. As of February 2026, Zod v3.24 remains the most popular runtime validation library in the Node.js ecosystem, with over 40 million weekly npm downloads. Why Zod for API Validation? You might be thinking: "I already use TypeScript. Isn't that enough?" No. TypeScript types are erased at runtime. When a POST request hits your Express server, TypeScript has zero idea what's inside req.body . It could be anything. Zod solves this by giving you: Runtime validation — actually checks the data at runtime Type inference