React 19 Server Actions vs API Routes in Next.js: When should you use which?

Question

With Server Actions (`'use server'`) built directly into Next.js App Router, do we still need standard API Route Handlers (`route.ts`)? What are the interview talking points on this?

Priya Sharma · Accepted Answer

Here is the exact distinction interviewers look for:

### 1. Use Server Actions When:
- **Mutating state from UI forms:** Form submissions, likes, comments, bookmark toggles, settings updates.
- **Progressive enhancement:** Works even before hydration completes.
- **Built-in revalidation:** You can call `revalidatePath('/dashboard')` or `revalidateTag('posts')` directly inside the action.
- **No URL boilerplate:** You don't need to invent arbitrary `/api/v1/update-profile` endpoints.

### 2. Use Route Handlers (`route.ts`) When:
- **External consumers:** Mobile apps, public REST APIs, third-party webhooks (e.g. Stripe, Razorpay webhook handlers).
- **Non-JSON responses:** Serving RSS feeds, dynamic XML sitemaps, PDFs, or raw file downloads.
- **Webhook verification:** When external services send raw POST payloads requiring cryptographic HMAC signature validation.

**Rule of thumb:** If the action is triggered by **your own user interface**, use **Server Actions**. If it is called by **an external system, third-party webhook, or mobile app**, use **Route Handlers**.

Arjun Mehta · Answer

Great explanation. Also remember Server Actions only support POST under the hood.

React 19 Server Actions vs API Routes in Next.js: When should you use which?

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