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.

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:

app/api/route.ts

export const runtime = 'edge'

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

ISR (Incremental Static Regeneration) is not supported in the Edge Runtime.

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

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:

proxy.ts

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

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.

Version history

Version	Changes
v12.0.0	Edge Runtime introduced