Next.js Route Handlers vs Server Actions

Next.js provides two main ways to execute server-side logic and handle data mutations from the client: Route Handlers (API routes) and Server Actions.

While both run on the server, they serve different architectural needs. Knowing when to use each is a common question in frontend interviews.

1. What are Route Handlers?

Route Handlers are custom request handlers that allow you to build REST-like API endpoints. They are defined in route.ts (or route.js) files and are accessed via standard HTTP requests (GET, POST, PUT, DELETE).

Code Example:

// app/api/users/route.ts
import { NextResponse } from "next/server";
 
export async function POST(request: Request) {
  const data = await request.json();
  const newUser = await db.user.create({ data });
  
  return NextResponse.json({ success: true, user: newUser }, { status: 201 });
}

Best Used For:

• Public APIs: When third-party apps or services need to access your data.
• Webhooks: Handling callbacks from services like Stripe, GitHub, or SendGrid.
• Mobile Clients: If you have a separate mobile app that needs standard JSON endpoints.
• Resource Streaming: Returning custom file downloads, PDF generation, or image assets.

2. What are Server Actions?

Server Actions are asynchronous functions declared with the "use server" directive. They allow client components to invoke server-side database code directly, behaving like a Remote Procedure Call (RPC). You do not write fetch API requests or declare custom route endpoints.

Code Example:

// app/actions.ts
"use server";
 
import { revalidatePath } from "next/cache";
 
export async function createUserAction(formData: FormData) {
  const email = formData.get("email") as string;
  await db.user.create({ data: { email } });
  
  // Revalidate the cache to show updated data instantly
  revalidatePath("/users");
}

You can import and trigger this function directly inside a client button or HTML form:

// app/components/UserForm.tsx
import { createUserAction } from "../actions";
 
export default function UserForm() {
  return (
    <form action={createUserAction}>
      <input name="email" type="email" required />
      <button type="submit">Register User</button>
    </form>
  );
}

Best Used For:

• Form Submissions: Standard application mutations (creating, updating, deleting database items).
• Next.js Internal Cache Mutations: Actions integrate deeply with revalidatePath and revalidateTag to update Next.js page caches dynamically.
• Quick UI Mutations: Small user updates like toggling a "like" button or updating settings.

Comparison Summary

Key Takeaways

• Route Handlers act as standard REST API endpoints. Use them when you need to serve public clients, webhooks, or mobile apps.
• Server Actions are internal RPC functions. Use them inside your Next.js application for forms, buttons, and state mutations.
• Server Actions simplify development by removing the need to write API endpoints and fetch client requests for basic database edits.
• Do not use Server Actions if third-party external applications need access to the endpoint; write a Route Handler instead.