What is the difference between a Route Handler and a Server Action? When would you choose one over the other?

Route Handlers are ideal when you need to expose functionality to external clients—whether that's your own frontend, third-party services, mobile apps, or webhook receivers. They give you full control over HTTP semantics: status codes, headers, caching directives, and response formats. You can stream responses, implement complex authentication, and version your API. Because they're public by design, you should always add appropriate authentication, rate limiting, and input validation. Route Handlers can be static or dynamic, cached or uncached, depending on your needs .

Server Actions are designed for one specific purpose: handling mutations that originate from your own UI. They're perfect for form submissions, button clicks, and any operation where you want to modify data and revalidate the cache. Unlike Route Handlers, Server Actions are not publicly callable—they can only be invoked from your components (or from other Server Actions). This makes them inherently more secure for operations that assume the user is already authenticated through your app's session. They integrate seamlessly with forms, support progressive enhancement, and automatically handle loading and error states when used with React's useTransition .

The choice between Route Handlers and Server Actions comes down to who needs to call your logic and how they'll call it. If you're building an endpoint for external consumption—mobile apps, third-party services, webhooks, or public APIs—use Route Handlers . If you're handling form submissions, button clicks, or any mutation that only your own UI will trigger, use Server Actions . For internal operations that need to be triggered from multiple places, Server Actions are cleaner and more integrated . The two can also work together: a Server Action might call an internal Route Handler, or a Route Handler might reuse business logic from a Server Action module .

The security posture differs significantly. Route Handlers are public endpoints—they must validate authentication/authorization on every request, typically via API keys, JWT tokens, or session cookies . Server Actions, being internal, can assume the user is already authenticated through your app's session (e.g., via middleware or layout checks) . However, you should still validate authorization inside Server Actions—don't trust that the UI prevented a button from rendering . Route Handlers need explicit CORS configuration if called from different origins; Server Actions never need CORS because they're called from your own components .