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When developing with Next.js, how do you validate the data that comes through API routes or forms? Unlike frameworks like Express or NestJS, Next.js doesn't provide a built-in validation layer. This means developers have to write their own code to ensure data integrity. In this post, I’ll show you how to integrate the familiar class-validator library—popular among NestJS developers—into a Next.js project. Step by step, we'll explore how you can write cleaner, more maintainable, and reliable validation logic using decorator-based validation. From my personal experience, introducing class-validator significantly improved both the stability of the product and the ease of development. While Next.js isn’t the most convenient tool for building APIs, a well-designed architecture can still make it a capable API server framework. This article is based on Next.js version 15. Please keep that in mind. 😉

As the React ecosystem evolves, Next.js offers developers a variety of rendering options. Notably, these include Next.js's Page Router SSR (Server-Side Rendering) and React Server Components (RSC). In this article, let's explore the differences between traditional Next.js Page Router-based SSR, Next.js App Router-based SSR, and React Server Components.