If you are learning Next.js, one of the most useful features you’ll meet early is API Routes in Next js. They let you write server-side code inside your Next.js app — for handling forms, talking to databases, or hiding secrets like API keys. In this guide I’ll walk you through what API Routes in Next js are, why and when to use them, how to build them step-by-step, and common pitfalls to avoid. I’ll keep things simple and friendly — like a short lesson in a Next js Course. In this article we focus on API Routes in Next js so you can build simple backends fast.

What are API Routes (in plain words)?

API Routes in Next js are small server endpoints you create inside your Next.js project. Instead of setting up a separate backend, you add files under pages/api (or app/api for the newer App Router) and Next.js serves them for you as server-side functions. You can receive HTTP requests (GET, POST, etc.), run logic, and return JSON or other responses. This makes it easy to keep frontend and backend together during learning or for small apps. If you are following a Next js Course, this is a great place to try full-stack ideas without a lot of setup.

When should you use next js api routes?

Use nextjs api routes when:

• You need a simple backend for forms, webhooks, or small data tasks.
  
• You want to keep your app and API in one repo (great for a Next js Course project).
  
• You need to keep secrets server-side (like API keys) and not expose them to the browser.
  

Do not use nextjs api routes as a replacement for a full, production API when your app needs heavy scaling or advanced features. For larger systems, consider a dedicated backend service. Serverless functions (how many providers run these routes) are convenient, but they can have limits such as cold starts or execution time.

How to create a basic API route (example)

Using the Pages Router (classic way), create a file at pages/api/hello.js and export a function:

// pages/api/hello.js

export default function handler(req, res) {

  res.status(200).json({ message: ‘Hello from API Routes in Next js!’ })

}

Now a request to /api/hello returns that JSON. This simple example shows how API Routes in Next js work and helps you test logic quickly.

App Router vs Pages Router: where to place route handlers

Next.js offers two router styles. If you use the Pages Router, create files under pages/api/* for API routes. If you use the App Router, create files like app/api/your-endpoint/route.js and export functions for GET or POST. The App Router uses route handlers that let you export GET, POST, PUT, or DELETE functions. Whichever router you use, learning both styles is useful in a Next js Course.

Handling different HTTP methods

In pages/api, you typically check req.method. In the App Router, you export specific functions such as export async function GET(req) {} or export async function POST(req) {}. Knowing how to handle methods helps you build robust nextjs api routes and return the correct status codes and messages.

Working with request bodies and files

By default, Next.js parses JSON bodies for you. If you need raw body handling — for example, to verify webhooks — you can disable parsing with:

export const config = { api: { bodyParser: false } }

and use libraries that read raw streams. For file uploads, either use middleware like multer or rely on external stores like S3. These details help you avoid common errors when building nextjs api routes.

Security tips (simple, must-know)

Keep secrets (API keys, DB passwords) in environment variables and never expose them to the client. API Routes in Next js run on the server and can read process.env safely. Always validate input and sanitize data. If your API might be called by other sites, add CORS rules. Treat every request as untrusted.

Avoid calling internal API routes from server-side rendering

A common beginner mistake is to call your own /api/* endpoints from getServerSideProps or other server code. That makes an extra HTTP request inside the same server. Instead, call shared functions directly from server code when possible. This reduces latency and avoids unnecessary overhead when using API Routes in Next js.

Testing and local development

Run npm run dev and test endpoints at http://localhost:3000/api/your-route. Use curl, Postman, or browser fetch to try GET and POST. Tools like Postman help you test nextjs api routes quickly. Write unit tests for handlers as your app grows. Using TypeScript gives better types for requests and responses and helps prevent bugs in nextjs api routes.

Deploying your API routes

When deployed to Vercel or similar platforms, nextjs api routes often run as serverless functions. They scale automatically but can have execution limits. For heavy background jobs or long tasks, use a separate backend or job queue. Understand the platform limits before moving critical work into API Routes in Next js.

Quick checklist for your Next js Course projects

• Choose pages/api or app/api based on your router.
  
• Keep secrets in env vars.
  
• Validate all inputs and handle errors cleanly.
  
• Avoid internal HTTP calls from server code.
  
• Test locally with Postman and write unit tests.
  
• Consider a dedicated backend when you need heavy processing.
  

Final thoughts

API Routes in Next js are a friendly way to learn backend ideas inside your frontend project. They are perfect for small apps, learning projects, and many real-world features like contact forms or simple APIs in a Next js Course. As you grow, learn when to move logic into a dedicated backend service. With practice, you’ll be comfortable building secure and useful nextjs api routes. Remember, nextjs api routes are great for learning and small projects — start small, learn the patterns, and build up from there.