The @layer0/core package provides a JavaScript API for controlling routing and caching from your code base rather than a CDN web portal. Using this "EdgeJS" approach allows this vital routing logic to be properly tested, reviewed, and version controlled, just like the rest of your application code.

Using the Router, you can:

  • Proxy requests to upstream sites
  • Send redirects from the network edge
  • Render responses on the server using Next.js, Nuxt.js, Angular, or any other framework that supports server side rendering.
  • Alter request and response headers
  • Send synthetic responses
  • Configure multiple destinations for split testing

To define routes for Layer0, create a routes.js file in the root of your project. You can override the default path to the router by setting the routes key in layer0.config.js.

The routes.js file should export an instance of @layer0/core/router/Router:

// routes.js
const { Router } = require('@layer0/core/router')

module.exports = new Router()

Declare routes using the method corresponding to the HTTP method you want to match.

// routes.js
const { Router } = require('@layer0/core/router')

module.exports = new Router().get('/some-path', ({ cache, proxy }) => {
  // handle the request here

All HTTP methods are available:

  • get
  • put
  • post
  • patch
  • delete
  • head

To match all methods, use match:

// routes.js
const { Router } = require('@layer0/core/router')

module.exports = new Router().match('/some-path', ({ cache, proxy }) => {
  // handle the request here

When Layer0 receives a request, it executes each route that matches the request in the order in which they are declared until one sends a response. The following methods return a response:

Multiple routes can therefore be executed for a given request. A common pattern is to add caching with one route and render the response with a later one using middleware. In the following example we cache then render a response with Next.js:

const { Router } = require('@layer0/core/router')
const { nextRoutes } = require('@layer0/next')

// In this example a request to /products/1 will be cached by the first route, then served by the `nextRoutes` middleware
new Router()
  .get('/products/:id', ({ cache }) => {
      edge: { maxAgeSeconds: 60 * 60, staleWhileRevalidateSeconds: 60 * 60 },

Layer0 offers APIs to manipulate request and response headers and cookies. The APIs are:

OperationRequestUpstream ResponseResponse sent to Browser
Set headersetRequestHeadersetUpstreamResponseHeadersetResponseHeader
Add cookie*addUpstreamResponseCookieaddResponseCookie
Update headerupdateRequestHeaderupdateUpstreamResponseHeaderupdateResponseHeader
Update cookie*updateUpstreamResponseCookieupdateResponseCookie
Remove headerremoveRequestHeaderremoveUpstreamResponseHeaderremoveResponseHeader
Remove cookie*removeUpstreamResponseCookieremoveResponseCookie

* Adding, updating, or removing a request cookie can be achieved with updateRequestHeader applied to cookie header.

You can find detailed descriptions of these APIs in the @layer0/core documentation

You can inject values from the request or response into headers or cookies as template literals using the ${value} format. For example: setResponseHeader('original-request-path', '${path}') would add an original-request-path response header whose value is the request path.

ValueEmbedded valueDescription
HTTP method${method}The value of the HTTP method used for the request (e.g. GET)
URL${url}The complete URL path including any query strings (e.g. /search?query=docs). Protocol, hostname, and port are not included.
Path${path}The URL path excluding any query strings (e.g. /search)
Query string${query:<name>}The value of the <name> query string or empty if not available.
Request header${req:<name>}The value of the <name> request header or empty if not available.
Request cookie${req:cookie:<name>}The value of the <name> cookie in cookie request header or empty if not available.
Response header${res:<name>}The value of the <name> response header or empty if not available.

The syntax for route paths is provided by path-to-regexp, which is the same library used by Express.

Named parameters are defined by prefixing a colon to the parameter name (:foo).

new Router().get('/:foo/:bar', res => {
  /* ... */

Please note: Parameter names must use "word characters" ([A-Za-z0-9_]).

Parameters can have a custom regexp, which overrides the default match ([^/]+). For example, you can match digits or names in a path:

new Router().get('/icon-:foo(\\d+).png', res => {
  /* ... */

Tip: Backslashes need to be escaped with another backslash in JavaScript strings.

Parameters can be wrapped in {} to create custom prefixes or suffixes for your segment:

new Router().get('/:attr1?{-:attr2}?{-:attr3}?', res => {
  /* ... */

It is possible to write an unnamed parameter that only consists of a regexp. It works the same the named parameter, except it will be numerically indexed:

new Router().get('/:foo/(.*)', res => {
  /* ... */

Modifiers must be placed after the parameter (e.g. /:foo?, /(test)?, /:foo(test)?, or {-:foo(test)}?).

Parameters can be suffixed with a question mark (?) to make the parameter optional.

new Router().get('/:foo/:bar?', res => {
  /* ... */

Tip: The prefix is also optional, escape the prefix \/ to make it required.

Parameters can be suffixed with an asterisk (*) to denote a zero or more parameter matches.

new Router().get('/:foo*', res => {
  /* will be an array */

The captured parameter value will be provided as an array.

Parameters can be suffixed with a plus sign (+) to denote a one or more parameter matches.

new Router().get('/:foo+', res => {
  /* will be an array */

The captured parameter value will be provided as an array.

Match can either take a URL path, or an object which allows you to match based on method, query parameters, cookies, and request headers:

    path: '/some-path', // value is route-pattern syntax
    method: /GET|POST/i, // value is a regular expression
    cookies: { currency: /^(usd)$/i }, // keys are cookie names, values are regular expressions
    headers: { 'x-moov-device': /^desktop$/i }, // keys are header names, values are regular expressions
    query: { page: /^(1|2|3)$/ }, // keys are query parameter names, values are regular expressions
  () => {},

The second argument to routes is a function that receives a ResponseWriter and uses it to send a response. Using ResponseWriter you can:

  • Proxy a backend configured in layer0.config.js
  • Serve a static file
  • Send a redirect
  • Send a synthetic response
  • Cache the response at edge and in the browser
  • Manipulate request and response headers

See the API Docs for Response Writer

This example shows typical usage of @layer0/core, including serving a service worker, next.js routes (vanity and conventional routes), and falling back to a legacy backend.

// routes.js

const { Router } = require('@layer0/core/router')

module.exports = new Router()
  .get('/service-worker.js', ({ serviceWorker }) => {
    // serve the service worker built by webpack
  .get('/p/:productId', ({ cache }) => {
    // cache products for one hour at edge and using the service worker
      edge: {
        maxAgeSeconds: 60 * 60,
        staleWhileRevalidateSeconds: 60 * 60,
      browser: {
        maxAgeSeconds: 0,
        serviceWorkerSeconds: 60 * 60,
  .fallback(({ proxy }) => {
    // serve all unmatched URLs from the origin backend configured in layer0.config.js

You can use the router's catch method to return specific content when the request results in an error status (For example, a 500). Using catch, you can also alter the statusCode and response on the edge before issuing a response to the user.

router.catch(number | Regexp, (routeHandler: Function))

To issue a custom error page when the origin returns a 500:

// routes.js

const { Router } = require('@layer0/core/router')

module.exports = new Router()
  // Example route
  .get('/failing-route', ({ proxy }) => {
  // So let's assume that backend "broken-origin" returns 500, so instead
  // of rendering the broken-origin response we can alter that by specifing .catch
  .catch(500, ({ serveStatic }) => {
    serveStatic('static/broken-origin-500-page.html', {
      statusCode: 502,

The .catch method allows the edge router to render a response based on the result preceeding routes. So in the example above whenever we receive a 500 we respond with broken-origin-500-page.html from the application's static directory and change the status code to 502.

  • Your catch callback is provided a ResponseWriter instance. You can use any ResponseWriter method except proxy inside .catch.
  • We highly recommend keeping catch routes simple. Serve responses using serveStatic instead of send to minimize the size of the edge bundle.

In addition to sending redirects at the edge within the router configuration, this can also be configured at the environment level within the Layer0 Developer Console.

Under <Your Environment> Configuration, click Edit to draft a new configuration. Scroll down to the Redirects section: redirects

Click Add A Redirect to configure the path or host you wish to redirect to: add redirect

Note: you will need to activate and redeploy your site for this change to take effect.