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What a Next.js BFF does—and what it does not
A Backend for Frontend sits between a user-facing application and the systems that supply its data or perform its work. In Next.js, server-side code can receive a request, validate it, call an upstream service, and return a response shaped for the frontend. This can keep private credentials out of client code and give the application a place to enforce access rules.
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The boundary matters: server-side execution does not make an endpoint private. A Route Handler is a public HTTP endpoint, and a Server Action invoked from the client must also be treated as an exposed operation. Next.js documentation puts the scope plainly: “Next.js backend capabilities are not a full backend replacement.” Next.js: Backend for Frontend.
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Which Next.js feature should handle the request?
| Need | Use | What to account for |
|---|---|---|
| A public HTTP endpoint, custom response, aggregation, or transformation | App Router Route Handler | Flexible HTTP methods and response types, but every handler is an API surface requiring validation and access controls. Next.js guidance; Route Handler reference. |
| Route or rewrite traffic to another backend | Proxy, rewrites, or a validating Route Handler proxy | Can keep internal service details out of client code; define which headers are forwarded and validate requests. Proxy alone does not authorize a user. Next.js guidance. |
| A frontend-triggered mutation | Server Action | Designed primarily for mutations. Authenticate, authorize, and validate each action; built-in protections are not a replacement for those checks. Next.js guidance; Data Security. |
| An API surface in an existing Pages Router app | API Route | Pages Router convention; the App Router uses Route Handlers instead. Next.js guidance. |
| Data needed to render a Server Component | Call the data source directly from the Server Component | A self-request to your own Route Handler adds an HTTP hop and can fail during build-time prerendering, when no application server is listening for that request. Next.js guidance. |
Route Handlers: the general-purpose HTTP boundary
In the App Router, define a Route Handler in a route.ts or route.js file. Supported methods include GET, POST, PUT, PATCH, DELETE, HEAD, and OPTIONS. Because clients other than your own UI can call the endpoint, implement its security and input checks as you would for any exposed API. See the Route Handler reference.
#1 Best Overall
Server Actions: for mutations, not a default data-fetching API
Server Actions run on the server but can be invoked by client code, so each action that reads or changes protected data needs its own authorization check. Next.js documents that actions are queued; using them for data fetching can therefore result in sequential execution. Use an HTTP endpoint or direct server-side data access when that better fits the request pattern.
Server Actions include protections such as non-deterministic action IDs and Origin-to-Host checks. Treat these as defense in depth, not permission checks. The Data Security guide also cautions against relying on encryption alone for values captured by closures.
Rank #2
Proxy and rewrites: routing is not authorization
Proxy or rewrites can direct requests to another service and reduce what needs to appear in client code. They do not by themselves prove who the caller is or whether that person may perform an operation. For sensitive work, enforce authentication and authorization at the endpoint or action that actually performs it, and make the header-forwarding boundary deliberate.
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Apply controls where each operation is performed. A hidden button, an earlier Proxy check, or the fact that code runs on a server is not a substitute for checks at the Route Handler or Server Action that accesses protected data.
- Authenticate and authorize every sensitive operation. Verify the caller’s identity and permission for the specific resource or action.
- Validate inputs. Check content type, size, structure, and values; reject malformed or unexpected requests. Sanitize data where the destination or use requires it.
- Limit abuse and resource use. Consider rate limits and timeouts for requests to your BFF and upstream services. Keep payload limits appropriate to the operation.
- Keep secrets on the server. Variables prefixed with
NEXT_PUBLIC_are exposed to the client, so do not use that prefix for credentials or other values that must remain private. See the Data Security guide. - Minimize disclosures. Return only data the caller is allowed to see, avoid exposing sensitive error details, and do not put unnecessary sensitive data in logs.
Server Action request-size and origin settings
The Next.js Server Actions configuration reference states a default maximum request body size of 1 MB; that page was last updated February 27, 2026. The limit can be configured, but raising it increases resource consumption, so match it to the payload your action actually needs. For deployments with reverse proxies or multiple backend layers, review the allowed-origin configuration rather than broadening it casually. See the Server Actions configuration reference.
When Server Components need data
For ordinary server-rendered page data, call the underlying database, service, or other data source from the Server Component instead of making an HTTP request to your own Route Handler. During build-time prerendering, there may be no running application server to receive a self-request. During on-demand rendering, the extra request adds an unnecessary network round trip. Keep a Route Handler when an actual HTTP boundary is needed—for example, when a client or external caller needs an endpoint—not merely to make server-side code call itself.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Check deployment limits before committing to the design
The framework’s deployment guide says Node.js server and Docker deployments support all Next.js features. Static export has limitations, and adapter support varies; a deployment target should be checked against the features the application uses. See Next.js deployment.
Some hosting platforms run handlers as lambdas. In that model, do not assume state can be shared across requests or that filesystem writes, long-running work, or WebSockets will be available. Confirm the chosen host’s runtime limits and timeouts before designing around those capabilities; “Next.js hosting” alone does not establish that every backend pattern will work.
Quick Recap
A practical decision path
- Rendering server-side page data? Call the underlying source directly from the Server Component.
- Need an HTTP endpoint for a browser or another client? Add an App Router Route Handler and treat it as public.
- Handling a user-triggered change? Use a Server Action where its mutation model fits, or a Route Handler where a conventional HTTP API is more appropriate. In either case, authorize at the operation boundary.
- Only need to route traffic? Consider Proxy or rewrites, but do not treat routing as permission enforcement; use a validating handler when the request needs application-level checks or transformation.
- Choosing a deployment target? Verify its runtime, request limits, timeout behavior, state model, filesystem access, and WebSocket support against the features you intend to use.
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