> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/vercel/next.js/llms.txt
> Use this file to discover all available pages before exploring further.

# Edge Runtime

> API reference for the Next.js Edge Runtime: supported APIs, restrictions, and how to use it in Middleware and Route Handlers.

Next.js provides two server runtimes:

* **Node.js Runtime** (default): full Node.js API surface, used for rendering and route handlers.
* **Edge Runtime**: a subset of Web APIs, optimized for low-latency responses at the edge. Used in [Middleware](/api-reference/file-conventions/middleware).

## Choosing a runtime

|                | Node.js | Edge                               |
| -------------- | ------- | ---------------------------------- |
| Cold start     | Slower  | Faster                             |
| Node.js APIs   | Full    | None                               |
| `node_modules` | All     | ES Modules only (no native addons) |
| Streaming      | Yes     | Yes                                |
| ISR            | Yes     | No                                 |

## Setting the runtime

Specify the runtime in a Route Handler or layout/page segment using the `runtime` export:

```ts app/api/route.ts theme={null}
export const runtime = 'edge'
```

The value must be `'edge'` or `'nodejs'`. When omitted, the Node.js runtime is used.

<Note>
  ISR (Incremental Static Regeneration) is not supported in the Edge Runtime.
</Note>

## Supported APIs

### Network APIs

| API               | Description                       |
| ----------------- | --------------------------------- |
| `Blob`            | Represents a blob                 |
| `fetch`           | Fetches a resource                |
| `FetchEvent`      | Represents a fetch event          |
| `File`            | Represents a file                 |
| `FormData`        | Represents form data              |
| `Headers`         | Represents HTTP headers           |
| `Request`         | Represents an HTTP request        |
| `Response`        | Represents an HTTP response       |
| `URLSearchParams` | Represents URL search parameters  |
| `WebSocket`       | Represents a WebSocket connection |

### Encoding APIs

| API                 | Description                          |
| ------------------- | ------------------------------------ |
| `atob`              | Decodes a base-64 encoded string     |
| `btoa`              | Encodes a string in base-64          |
| `TextDecoder`       | Decodes a `Uint8Array` into a string |
| `TextDecoderStream` | Chainable decoder for streams        |
| `TextEncoder`       | Encodes a string into a `Uint8Array` |
| `TextEncoderStream` | Chainable encoder for streams        |

### Stream APIs

| API                           | Description                           |
| ----------------------------- | ------------------------------------- |
| `ReadableStream`              | Represents a readable stream          |
| `ReadableStreamBYOBReader`    | Reader for a `ReadableStream`         |
| `ReadableStreamDefaultReader` | Default reader for a `ReadableStream` |
| `TransformStream`             | Represents a transform stream         |
| `WritableStream`              | Represents a writable stream          |
| `WritableStreamDefaultWriter` | Writer for a `WritableStream`         |

### Crypto APIs

| API            | Description                                                       |
| -------------- | ----------------------------------------------------------------- |
| `crypto`       | Access to platform cryptographic functions                        |
| `CryptoKey`    | Represents a cryptographic key                                    |
| `SubtleCrypto` | Low-level cryptographic primitives (hashing, signing, encryption) |

### Web Standard APIs

All standard JavaScript globals are available: `Array`, `ArrayBuffer`, `Boolean`, `Date`, `Error`, `JSON`, `Map`, `Math`, `Number`, `Object`, `Promise`, `Proxy`, `RegExp`, `Set`, `String`, `Symbol`, `URL`, `URLPattern`, `URLSearchParams`, `WeakMap`, `WeakSet`, `WebAssembly`, timer functions (`clearInterval`, `clearTimeout`, `setInterval`, `setTimeout`), encoding helpers (`decodeURI`, `decodeURIComponent`, `encodeURI`, `encodeURIComponent`), typed arrays, `AbortController`, `console`, `DOMException`, `queueMicrotask`, `structuredClone`, and more.

### Next.js polyfills

* `AsyncLocalStorage` (Node.js `async_hooks` API)

### Environment variables

```ts theme={null}
const value = process.env.MY_VAR
```

`process.env` is available in both `next dev` and `next build`.

## Unsupported APIs

The following are **not available** in the Edge Runtime:

* Native Node.js APIs (filesystem, `crypto` module, `Buffer`, etc.)
* CommonJS `require()` — use ES module `import` instead
* `node_modules` packages that use native Node.js APIs

The following JavaScript features are also disabled:

| API                       | Description                                           |
| ------------------------- | ----------------------------------------------------- |
| `eval`                    | Evaluates a JavaScript string as code                 |
| `new Function(code)`      | Creates a function from a string                      |
| `WebAssembly.compile`     | Compiles a WASM module from a buffer                  |
| `WebAssembly.instantiate` | Compiles and instantiates a WASM module from a buffer |

## Allowing dynamic code evaluation

In rare cases where code contains unreachable dynamic evaluation, you can suppress the build error using `unstable_allowDynamic` in your Proxy config:

```ts proxy.ts theme={null}
export const config = {
  unstable_allowDynamic: [
    '/lib/utilities.js',
    '**/node_modules/function-bind/**',
  ],
}
```

<Warning>
  If the allowed statements are executed at runtime on the Edge, they will throw a runtime error. Use `unstable_allowDynamic` only for code paths that are guaranteed not to execute.
</Warning>

## Version history

| Version   | Changes                 |
| --------- | ----------------------- |
| `v12.0.0` | Edge Runtime introduced |