Configuration API

Cypress enables you to dynamically modify configuration values and environment variables from your plugin file.


To modify configuration, you return an object from your plugins file exported function.

// cypress/plugins/index.js
module.exports = (on, config) => {
  console.log(config) // see what all is in here!

  // modify config values
  config.defaultCommandTimeout = 10000
  config.baseUrl = 'https://staging.acme.com'

  // modify env var value
  config.env.ENVIRONMENT = 'staging'

  // return config
  return config

Whenever you return an object from your pluginFile, Cypress will take this and “diff” it against the original configuration and automatically set the resolved values to point to what you returned.

If you don’t return an object, then configuration will not be modified.

The config object also includes the following extra values that are not part of the standard configuration. These values are read only and cannot be modified from the plugins file.

  • configFile: The absolute path to the config file. By default, this is <projectRoot>/cypress.json, but may be a custom path or false if using the --config-file flag.
  • projectRoot: The absolute path to the root of the project (e.g. /Users/me/dev/my-project)

Resolved values will show up in the “Settings” tab of the Test Runner.

Resolved configuration in the Desktop app


Additionally, Cypress will respect and await promises you return. This enables you to perform asynchronous tasks and eventually resolve with the modified configuration object. See the example on switching between multiple configuration files for a full example.


Customize available browsers

The configuration includes the list of browsers found on your system that are available to Cypress.

Read our full guide on Launching Browsers for more information on how this works.

In the plugins file, you can filter the list of browsers passed inside the config object and return the list of browsers you want available for selection during cypress open.

// cypress/plugins/index.js
module.exports = (on, config) => {
  // inside config.browsers array each object has information like
  // {
  //   name: 'chrome',
  //   family: 'chromium',
  //   channel: 'canary',
  //   displayName: 'Canary',
  //   version: '80.0.3966.0',
  //   path:
  //    '/Applications/Canary.app/Contents/MacOS/Canary',
  //   majorVersion: 80
  // }
  return {
    browsers: config.browsers.filter((b) => b.family === 'chromium')

When you open the Test Runner in a project that uses the above modifications to your plugins file, only the Chrome browsers found on the system will display in the list of available browsers.

Filtered list of Chrome browsers

If you return an empty list of browsers or browsers: null, the default list will be restored automatically.

If you modify the list of browsers, you can see the resolved configuration in the Settings tab of the Test Runner.

Switch between multiple configuration files

This means you can do things like store multiple configuration files and switch between them like:

  • cypress.qa.json
  • cypress.dev.json
  • cypress.prod.json

How you choose to organize your configuration and environment variables is up to you.

// promisified fs module
const fs = require('fs-extra')
const path = require('path')

function getConfigurationByFile (file) {
  const pathToConfigFile = path.resolve('..', 'config', `${file}.json`)

  return fs.readJson(pathToConfigFile)

// plugins file
module.exports = (on, config) => {
  // accept a configFile value or use development by default
  const file = config.env.configFile || 'development'

  return getConfigurationByFile(file)

You could now swap out configuration + environment variables like so:

cypress run
cypress run --env configFile=qa
cypress run --env configFile=staging
cypress run --env configFile=production

Each of these environments would read in the configuration at these files:


This would enable you to do things like this:

// cypress/config/development.json

  "baseUrl": "http://localhost:1234",
  "env": {
    "something": "development"
// cypress/config/qa.json

  "baseUrl": "https://qa.acme.com",
  "env": {
    "something": "qa"
// cypress/config/staging.json

  "baseUrl": "https://staging.acme.com",
  "env": {
    "something": "staging"
// cypress/config/production.json

  "baseUrl": "https://production.acme.com",
  "env": {
    "something": "production"

This is a less complicated example. Remember - you have the full power of Node at your disposal.

How you choose to edit the configuration is up to you. You don’t have to read off of the file system - you could store them all in memory inside of your pluginsFile if you wanted.

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Licensed under the MIT License.