Next.js 15 Fullstack Web Apps · Lesson

Building API Route Handlers

Create robust RESTful API endpoints using the App Router's Route Handlers for backend logic.

Building API Route Handlers is a free Next.js 15 Fullstack Web Apps lesson on CoddyKit — lesson 1 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Next.js 15 Fullstack Web Apps learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome to Route Handlers

In Next.js 15, Route Handlers are the powerful way to build backend API endpoints directly within your App Router project.

They allow you to create RESTful APIs, handle webhooks, or perform any server-side logic, all co-located with your frontend code.

Why Use Route Handlers?

Route Handlers offer several benefits:

Simplicity: No need for a separate backend server.
Co-location: API logic lives next to related UI components.
Performance: Built on Web Standard APIs, making them efficient.
Flexibility: Support all HTTP methods (GET, POST, PUT, DELETE, etc.).

Creating Your First Handler

To create a Route Handler, define a route.ts (or .js) file inside an app directory segment. For example, app/api/hello/route.ts will handle requests to /api/hello.

Inside this file, you export functions that match HTTP methods, like GET, POST, etc.

Handling GET Requests

The GET function handles HTTP GET requests. It receives a NextRequest object and should return a NextResponse.

Let's create a simple 'hello world' API endpoint.

import { NextResponse } from 'next/server';

export async function GET() {
  return NextResponse.json({ message: 'Hello from API!' });
}

How to Access GET Handler

The previous code snippet, placed in app/api/hello/route.ts, creates an endpoint accessible at /api/hello.

When you navigate to http://localhost:3000/api/hello in your browser, you'll see the JSON response: {"message":"Hello from API!"}.

Handling POST Requests

For data submission, you'll use the POST function. It also receives the NextRequest object, which contains the request body.

You can parse the JSON body using await request.json().

import { NextRequest, NextResponse } from 'next/server';

export async function POST(request: NextRequest) {
  const data = await request.json();
  return NextResponse.json(
    { message: 'Data received', data },
    { status: 200 }
  );
}

Accessing Request Details

The NextRequest object provides rich access to request details:

request.url: The full request URL.
request.headers: Request headers (e.g., request.headers.get('Content-Type')).
request.nextUrl.searchParams: Query parameters (e.g., ?name=Alice).

These are crucial for dynamic and secure API logic.

Dynamic Segments in Handlers

Just like pages, Route Handlers can have dynamic segments. For example, app/api/items/[id]/route.ts.

You can access these dynamic parameters from the params object passed to your handler function.

import { NextRequest, NextResponse } from 'next/server';

interface Params {
  params: { id: string };
}

export async function GET(
  request: NextRequest,
  { params }: Params
) {
  const id = params.id; // '123' for /api/items/123
  return NextResponse.json({ itemId: id, message: 'Fetched item' });
}

Setting Status and Headers

When returning a NextResponse, you can customize the HTTP status code and headers.

This is important for proper API communication, like indicating success (200, 201) or errors (400, 404, 500).

import { NextResponse } from 'next/server';

export async function DELETE() {
  return new NextResponse(null, { status: 204 }); // No Content
}

Quick Check: Handler Basics

You want to create an API endpoint at /api/products that returns a list of products when a GET request is made.

Which code snippet correctly sets up this handler in app/api/products/route.ts?

Recap: Building API Handlers

You've learned the fundamentals of Next.js 15 Route Handlers!

They allow backend logic co-located in the app directory.
Define handlers by exporting functions (GET, POST, etc.) in a route.ts file.
Use NextRequest to access request details and NextResponse to send responses.
Dynamic segments enable flexible API routes.

This powerful feature streamlines fullstack development in Next.js.

Frequently asked questions

Is the “Building API Route Handlers” lesson free?

Yes — the full text of “Building API Route Handlers” is free to read here on the web, and the Next.js 15 Fullstack Web Apps course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Next.js 15 Fullstack Web Apps course, upgrade to CoddyKit PRO.

What will I learn in “Building API Route Handlers”?

Create robust RESTful API endpoints using the App Router's Route Handlers for backend logic. You practise Next.js 15 Fullstack Web Apps with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Next.js 15 Fullstack Web Apps?

No prior experience is required. Next.js 15 Fullstack Web Apps on CoddyKit is structured for beginners through advanced learners; this is — lesson 1 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Building API Route Handlers” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Next.js 15 Fullstack Web Apps lesson?

Yes. Every Next.js 15 Fullstack Web Apps lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

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