Prerequisite Knowledge

What Is Next.js? The Beginner’s Guide

Why Next.js suits SaaS: routing, SSR/SSG, and API routes in one repo — a beginner-friendly, full-length guide.

What Is Next.js? The Beginner’s Guide

Next.js is a framework built on React and Node.js that makes it easier to develop modern web applications (overview). In a nutshell, Next.js provides an all-in-one solution for building rich SaaS (Software-as-a-Service) platforms by combining the front-end and back-end in a single project. It offers features like built-in routing, server-side rendering (SSR), static site generation (SSG), and API routes out-of-the-box, so you can focus on your app’s functionality rather than boilerplate setup (why developers use Next.js). This combination of capabilities is exactly why Next.js has become popular for SaaS apps – you get fast page loads, SEO-friendly pages, and backend endpoints all in one codebase.

What Next.js Provides Out of the Box

One of the biggest advantages of Next.js is how much it delivers with zero configuration. Here are some key features Next.js provides by default:

File-Based Routing: You don’t need to set up a separate router or use React Router – Next.js automatically creates routes based on your files and folders (file-based routing). For example, a file named pages/about.js becomes the /about page of your app. This convention makes organizing pages intuitive and eliminates manual route definitions.

Server-Side Rendering (SSR): Next.js can render pages on the server for each request, sending fully formed HTML to the client (SSR basics). This means faster initial load times and better SEO, since search engines can index your content easily. After the server renders the HTML, React takes over (“hydrates” the page) on the client for interactivity.

Static Site Generation (SSG): For pages that don’t need to be dynamic on every request, Next.js can pre-build them as static files at build time (SSG). These pages load extremely fast (and are also SEO-friendly) because they’re just served from a CDN or web server without needing a live render on each visit. SSG is great for marketing pages, documentation, or any content that updates infrequently.

Built-in API Routes: Next.js allows you to create backend endpoints by simply adding files in an api directory (API routes). These API routes run on a Node.js server (or serverless function) as part of your Next.js app. You can handle form submissions, database queries, authentication, etc., without spinning up a separate Express server – the API lives in the same project as your frontend. (We’ll explore this more in a section below.)

Automatic Code Splitting & Optimization: Next.js automatically splits your JavaScript bundle by page and optimizes assets (optimizations). Each page only loads the JS and CSS it truly needs, rather than one giant bundle. This results in faster page loads and better performance for your users. Next.js also comes with production optimizations like minification, tree-shaking, and image optimization built-in. You don’t have to configure Webpack or Babel – it’s handled for you.

Zero-Config Developer Experience: Beyond the big features, Next.js supports TypeScript out-of-the-box, has built-in CSS and Sass support, and integrates with popular libraries (for state, styling, data fetching, etc.) seamlessly (DX overview). The goal is that you can start coding your app’s features immediately, with minimal setup.

In short, Next.js gives you a full-stack React framework. All the heavy lifting for routing, bundling, and rendering is solved for you, so “all you have to do is write your React components” (discussion). This is a huge win for SaaS developers: you can build your product faster and know that the fundamentals (like fast loading and SEO support) are already taken care of.

Routing Model and Layouts in Next.js

Next.js uses a file-based routing system that maps your folder structure to URL paths. Each file or folder in the pages (or new app) directory automatically becomes a route. For example, a nested folder structure like pages/user/settings/notifications.js will generate a URL path /user/settings/notifications. This built-in router eliminates the need for manual route configuration and keeps your URL structure consistent with your project structure.

Defining routes in Next.js is as simple as creating files. You organize pages by directories, and Next.js turns that into navigable URLs. This model covers dynamic routes too – for instance, a file named [id].js in the pages/posts/ folder becomes a route like /posts/123 for a blog post with ID 123. Under the hood, Next.js handles all the linking and code-splitting for these routes, so clicking from one page to another is snappy and doesn’t reload the whole site.

Next.js also introduces the concept of layouts to manage repeated page sections. In traditional React apps, you might wrap pages with layout components (for headers, footers, sidebars). Next.js 13’s new App Router makes this even easier by allowing nested layouts defined at the folder level. For example, you could create an app/dashboard/layout.js file that defines a dashboard sidebar and header – all pages under /dashboard/* would automatically use that layout. This means you can have consistent navigation chrome (like a sidebar on all dashboard pages) without manually wrapping each page (nested layouts). Layouts help structure SaaS applications by keeping common UI in one place; you might have one layout for public marketing pages and another for the logged-in user’s app interface.

In plain terms, Next.js routing and layouts let you build multi-page apps without pain. You get a clean URL structure (important for user-friendliness and SEO) and the ability to maintain common page elements easily. You don’t have to fiddle with external routing libraries or worry about mounting/unmounting layout components – Next.js takes care of it in a convention-over-configuration style.

Server Components vs. Client Components (Plain English)

As a beginner using Next.js (especially version 13 and above), you might come across the terms Server Component and Client Component. This is related to how Next.js and React handle rendering. Let’s break it down in simple terms:

Server Components are pieces of your React app that run on the server (before the user’s browser gets anything). They render their content to HTML on the server and send that HTML down to the browser. Importantly, no React JS code for those components is sent to the browser (server vs client components). This makes them super fast and great for things like displaying data (since they can fetch data directly on the server) or content that doesn’t require interactivity. Think of a server component as a snippet of UI that is pre-made on the server – the user just sees the ready-made HTML. It’s also secure, because any sensitive data stays on the server. However, server components cannot handle user interactions (no onClick events, no dynamic updates in the browser) by themselves, since they don’t include client-side JavaScript.

Client Components are the traditional React components that run in the browser. These are needed for anything interactive – if you have a button that triggers a popup, a form that users type into, or any UI that updates after the page loads, those parts need to be client components. They do come with JavaScript that loads in the browser to make them work (client components). This means client components enable rich interactivity (handling clicks, input, animations, etc.), but they also make the bundle size larger and initial page load a bit slower compared to pure HTML. In Next.js, you designate a component to be a client component by adding a special directive at the top of the file: "use client".

In practice, a Next.js page can be composed of both types: perhaps the non-interactive framework of the page is a server component (for fast load and SEO), and specific interactive widgets inside it are client components. This hybrid approach gives you the best of both – you get the performance and SEO benefits of server-rendered content, alongside the dynamic behavior of React on the client. For example, on a SaaS dashboard page, you might render the bulk of the data and layout via server components (so the user sees content immediately and securely), but use a client component for a chart that allows zooming or a form that submits data.

The key takeaway for a beginner: Server Components = rendered on the server (no JS on client, good for static content and speed), Client Components = rendered in the browser (needed for interactivity). Next.js defaults to server components for most parts (to optimize performance), and you opt-in to client components when necessary. You don’t need to deep-dive into the technicalities right away, but it’s useful to know why Next.js asks you to mark some components with "use client" – it’s so you include only what you truly need in the browser. This separation is one of Next.js’s superpowers for balancing speed and richness in a SaaS app.

Built-in API Routes: Your Backend in the Same Repo

One standout Next.js feature for SaaS development is API routes. Normally, to build a backend for your application, you might create a separate server (for example, a Node/Express app or a Nest.js service) to handle data fetching, form processing, authentication, etc. With Next.js, you can often skip that extra setup – Next.js lets you define backend endpoints alongside your front-end pages.

In a Next.js project, any file you put under the pages/api/ directory (in the Pages Router) or under app/api/ (in the App Router) becomes an HTTP endpoint. For example, you could create pages/api/hello.js with the following code:

// pages/api/hello.js
export default function handler(req, res) {
  res.status(200).json({ greeting: "Hello from Next API" });
}

Now, if your app is running, a request to /api/hello will execute that handler function on the server and return { "greeting": "Hello from Next API" } as JSON. This is incredibly powerful – it means your React front-end and your API can live in the same codebase. You can create endpoints for things like retrieving user info, saving a form, or checking system health, all without deploying a separate server. In fact, when deployed to platforms like Vercel, these API routes become serverless functions automatically.

Next.js API routes allow you to build a SaaS without a separate backend for many cases. For instance, at startup phase you might have Next.js pages for your UI and Next.js API routes for your data needs (talking to a database or third-party services). They can share code, config, and types with your front-end, making development faster and more cohesive. And since the API routes run on the server side, you can keep secrets (API keys, database credentials) safe and out of the client’s reach.

It’s worth noting that using API routes does not bloat your client-side bundle – the code in pages/api is never sent to the browser (API routes are server-only). It runs only on the server. So you get the benefit of a backend without burdening your front-end.

To give a concrete example, imagine you’re building a SaaS and want a quick health check endpoint (perhaps for monitoring or just to show that your backend is working). You can create api/health.js that returns something like { status: "ok" }. When you run your app and visit http://localhost:3000/api/health, you’ll see that JSON response. In fact, go ahead and try it: run pnpm dev in your Next.js project and open /api/health in your browser to see a live API route in action. 🎉 It’s a simple way to confirm that your Next.js app is serving backend logic. (This could serve as a quick proof that you don’t need a separate server just to get an API up and running!)

Of course, as your SaaS grows, you might integrate with external databases or need more complex backend logic. Next.js API routes can call those databases or even call external APIs. And if one day you outgrow the built-in API routes, you can always set up a dedicated backend service. But many teams find that Next.js API routes cover a lot of use cases for small to medium applications.

Tradeoffs: When You Might Not Need Next.js

With all these features, you might be wondering: Is Next.js always the right choice? It’s a great tool, but it’s important to know the tradeoffs and scenarios where it might be overkill.

Is Next.js overkill for simple projects? If you’re building an extremely simple site – say a single landing page or a very basic static website – Next.js can feel like more framework than you actually need. You might not require features like SSR or API routes at all for a tiny project. In such cases, a simpler setup (like plain React with Vite, or even just static HTML) could suffice. Next.js does have a bit of learning curve and additional build steps that purely static sites don’t. That said, Next.js is designed to scale with you. While it might be overkill for a one-page site, it won’t hurt if you use it for one – and if that site later grows into a complex app, you’ll be glad to have Next.js’s capabilities ready. As one analysis put it, Next.js “might feel like overkill for extremely simple projects,” but as your project scales, its benefits will outweigh the initial setup overhead (is it overkill?). In other words, you can comfortably start small with Next.js, and it will support you as your app demands grow. Many developers choose Next.js even for moderately simple sites just to avoid re-tooling later.

Can you build a SaaS without a separate backend? Yes – in fact, many do. Next.js’s integrated API routes mean that for a lot of SaaS applications, you don’t need a separate server at the start. Your Next.js app can handle the frontend React UI and also serve JSON data or handle form submissions via API routes. For example, the team behind sushi-templates.com uses Next.js for the entire stack (both the user-facing pages and the backend logic live in one Next.js codebase). This unified approach can simplify development and deployment: you deploy one app, and everything (UI + API) is in sync. According to community answers, there’s nothing wrong with using a separate backend if you prefer – you can absolutely call external APIs from your Next.js app – but it’s often easier to start with API routes and no extra backend unless your use-case demands it (separate backend?). By keeping everything in one repo, you avoid the complexity of managing CORS, syncing data models across projects, or deploying multiple services.

Of course, there are cases where a dedicated backend service might be necessary or beneficial: for example, heavy data processing, specialized microservices, or a scenario where you have multiple different front-ends consuming the same API. In those situations, you might introduce a separate backend (like an Express API or a cloud function) in addition to Next.js. The good news is Next.js is flexible – you can use API routes for some things and still fetch from an external service for others. There’s no rule that it’s all or nothing.

When might you not need Next.js at all? If your application doesn’t need server-rendering for SEO or doesn’t benefit from the file-based routing and you’re just building a very interactive client-side app (like a purely internal tool or a game), you could stick with a simpler React setup. Next.js does introduce some constraints (you follow its conventions) and some overhead (build process, deployment considerations), so for a quick prototype or embed widget, plain React might be lighter. Also, if you already have a complete separate backend and you only need a frontend that will be entirely client-side rendered, using Next.js is still fine – but some teams in that scenario opt for something like Create React App or Vite + React, especially if SEO is a non-issue and they want total freedom on configuration. In essence, Next.js shines when you want an opinionated, full-stack framework; if your needs are extremely simple or extremely unique, those opinions might feel restricting.

In summary, Next.js is a powerful choice for most web apps and certainly for SaaS products due to its holistic approach. It might be “overkill” for a static one-pager, but it’s hardly a bad choice – and it positions you well for future growth. And yes, you can absolutely build a SaaS without a separate backend when using Next.js – plenty of companies and indie makers do just that, leveraging Next.js to handle everything in one place (backend options). The framework’s ability to bridge front-end and back-end in one project is a game-changer for developer productivity (why it’s a game-changer).

Conclusion & Next Steps

Next.js offers a beginner-friendly yet powerful way to build web applications. It streamlines development by providing routing, rendering optimizations, and backend capabilities right out-of-the-box. For someone building a SaaS, this means you can get your idea online faster and with fewer moving parts. You don’t have to reinvent the wheel for common needs – Next.js has got you covered with a solid foundation.

If you’re ready to give Next.js a try, a great first step is to run a development server and poke around one of its features. For example, if you have a Next.js project set up (you can use npx create-next-app@latest or a template provided by your team), start it with pnpm dev. Then open your browser to http://localhost:3000/api/health (assuming you’ve created an api/health route as described). You should see a response from your API route, such as a JSON message. This simple action confirms that your Next.js app is serving both the frontend and backend logic together – pretty cool, right?

From here, you can start building out pages and adding more API routes to flesh out your SaaS. Use file-based routing to create new pages, use server components for fast-loading content, and sprinkle in client components for interactivity. Next.js will handle the heavy lifting behind the scenes.

Happy coding, and welcome to the Next.js world – where your React skills go further, and building a full-stack SaaS becomes a delight instead of a headache!

References

SaaS 101: What 'Software as a Service' Really Means

An introduction to the Software‑as‑a‑Service (SaaS) model — understanding what SaaS means, how it works, its key benefits, and why it's become a dominant way to deliver software in the cloud era.

What Is Middleware? A Beginner-Friendly Guide

Understand middleware from first principles, why SaaS apps use it, and how our Next.js middleware works with i18n and request IDs — plus how to customize it.

On this page

What Is Next.js? The Beginner’s Guide
What Next.js Provides Out of the Box
Routing Model and Layouts in Next.js
Server Components vs. Client Components (Plain English)
Built-in API Routes: Your Backend in the Same Repo
Tradeoffs: When You Might Not Need Next.js
Conclusion & Next Steps
References