Next.js vs React: what is the difference?
React is a library for building user interfaces. Next.js is a full framework built on top of React that adds the things a real website needs, like routing, server rendering, and performance features. So it is not really React versus Next.js. Next.js is React, with more included.
Here is what that means for your product.
What plain React gives you
React handles the interface: the buttons, forms, and screens. On its own, it does not decide how pages are routed, how they are rendered for search engines, or how the site is served. You add those pieces yourself. That is fine for an app that lives behind a login where search visibility does not matter.
What Next.js adds
Next.js includes routing, server-side rendering, static generation, and image and performance tooling out of the box. Two things matter most for founders:
SEO. Next.js can render pages on the server, so search engines and AI crawlers see real content. Plain React apps often render in the browser, which is worse for ranking.
Speed and structure. You get a sensible structure and good performance defaults without wiring it all up yourself.
Which should you use?
Use Next.js if your product has public pages that need to rank, like a marketing site, a blog, or a marketplace. That covers most SaaS products.
Use plain React if the product is entirely a private app behind a login, where SEO is irrelevant and you want maximum flexibility.
For most founders, Next.js is the safer default. It does not lock you out of anything, and it solves problems you would otherwise hit later.
I build with both. See my web app development service, or read about the best stack for a SaaS MVP.