Browser Launch API

Before Cypress launches a browser, it gives you the opportunity to modify the browser preferences, install extensions, add and remove command-line arguments, and modify other options from the setupNodeEvents function.

Syntax

caution

⚠️ This code is part of the setupNodeEvents function and thus executes in the Node environment. You cannot call Cypress or cy commands in this function, but you do have the direct access to the file system and the rest of the operating system.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        /* ... */
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        /* ... */
      })
    },
  },
})

browser (object)

An object describing the browser being launched, with the following properties:

Property	Type	Description
`name`	`string`	Machine-friendly name, like `chrome`, `electron`, `edge`, or `firefox`.
`family`	`string`	Rendering engine being used. `chromium` or `firefox`.
`channel`	`string`	Release channel of the browser, such as `stable`, `dev`, or `canary`.
`displayName`	`string`	Human-readable display name for the browser.
`version`	`string`	Full version.
`path`	`string`	Path to the browser on disk. Blank for Electron.
`info`	`string`	(Optional) Extra information about the browser (used for display in the browser selector)
`majorVersion`	`number`	The major version number of the browser.
`isHeadless`	`boolean`	Whether the browser is running headlessly.
`isHeaded`	`boolean`	Whether the browser displays headed.

launchOptions (object)

Options that can be modified to control how the browser is launched, with the following properties:

Property	Type	Description
`preferences`	`object`	An object describing browser preferences. Differs between browsers. See Changing browser preferences for details.
`args`	`string[]`	An array of strings that will be passed as command-line args when the browser is launched. Has no effect on Electron. See Modify browser launch arguments for details.
`extensions`	`string[]`	An array of paths to folders containing unpacked WebExtensions to be loaded before the browser starts. Note: Electron currently only supports Chrome DevTools extensions. See Add browser extensions for details.
`env`	`object`	An object of environment variables to pass to the launched browser. See Configure browser environment for details.

Usage

Modify browser launch arguments, preferences, extensions, and environment

Using the setupNodeEvents function you can tap into the before:browser:launch event and modify how Cypress launches the browser (e.g. modify arguments, user preferences, and extensions).

This event will yield you the browser object, which gives you information about the browser, and the launchOptions object, which allows you to modify how the browser is launched.

The returned launchOptions object will become the new launch options for the browser.

Modify browser launch arguments:

Here are args available for the currently supported browsers:

Open devtools by default

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        // `args` is an array of all the arguments that will
        // be passed to browsers when it launches
        console.log(launchOptions.args) // print all current args

        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // auto open devtools
          launchOptions.args.push('--auto-open-devtools-for-tabs')
        }

        if (browser.family === 'firefox') {
          // auto open devtools
          launchOptions.args.push('-devtools')
        }

        if (browser.name === 'electron') {
          // auto open devtools
          launchOptions.preferences.devTools = true
        }

        // whatever you return here becomes the launchOptions
        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        // `args` is an array of all the arguments that will
        // be passed to browsers when it launches
        console.log(launchOptions.args) // print all current args

        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // auto open devtools
          launchOptions.args.push('--auto-open-devtools-for-tabs')
        }

        if (browser.family === 'firefox') {
          // auto open devtools
          launchOptions.args.push('-devtools')
        }

        if (browser.name === 'electron') {
          // auto open devtools
          launchOptions.preferences.devTools = true
        }

        // whatever you return here becomes the launchOptions
        return launchOptions
      })
    },
  },
})

Add browser extensions:

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        // supply the absolute path to an unpacked extension's folder
        // NOTE: extensions cannot be loaded in headless Chrome
        launchOptions.extensions.push('Users/jane/path/to/extension')

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        // supply the absolute path to an unpacked extension's folder
        // NOTE: extensions cannot be loaded in headless Chrome
        launchOptions.extensions.push('Users/jane/path/to/extension')

        return launchOptions
      })
    },
  },
})

Configure browser environment:

caution

This option is not supported when targeting Electron.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        launchOptions.env.CUSTOM_ENV_VALUE = '1'

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        launchOptions.env.CUSTOM_ENV_VALUE = '1'

        return launchOptions
      })
    },
  },
})

Changing browser preferences:

Here are preferences available for the currently supported browsers:

Chromium-based browsers
Electron
Firefox: visit about:config URL within your Firefox browser to see all available preferences.

info

If you want to ignore Chrome preferences altogether, you can set IGNORE_CHROME_PREFERENCES as an environment variable when running Cypress.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // in Chromium, preferences can exist in Local State, Preferences, or Secure Preferences
          // via launchOptions.preferences, these can be acccssed as `localState`, `default`, and `secureDefault`

          // for example, to set `somePreference: true` in Preferences:
          launchOptions.preferences.default['preference'] = true

          return launchOptions
        }

        if (browser.family === 'firefox') {
          // launchOptions.preferences is a map of preference names to values
          launchOptions.preferences['some.preference'] = true

          return launchOptions
        }

        if (browser.name === 'electron') {
          // launchOptions.preferences is a `BrowserWindow` `options` object
          launchOptions.preferences.darkTheme = true

          return launchOptions
        }
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // in Chromium, preferences can exist in Local State, Preferences, or Secure Preferences
          // via launchOptions.preferences, these can be acccssed as `localState`, `default`, and `secureDefault`

          // for example, to set `somePreference: true` in Preferences:
          launchOptions.preferences.default['preference'] = true

          return launchOptions
        }

        if (browser.family === 'firefox') {
          // launchOptions.preferences is a map of preference names to values
          launchOptions.preferences['some.preference'] = true

          return launchOptions
        }

        if (browser.name === 'electron') {
          // launchOptions.preferences is a `BrowserWindow` `options` object
          launchOptions.preferences.darkTheme = true

          return launchOptions
        }
      })
    },
  },
})

Modify Electron app switches

The Cypress Launchpad is an Electron application, and its behavior (and the behavior of the bundled-in Electron browser) can be customized using command line switches. The supported switches depend on the Electron version, see Electron documentation.

You can pass Electron-specific launch arguments using the ELECTRON_EXTRA_LAUNCH_ARGS environment variable. For example, to disable HTTP browser cache and ignore certificate errors, you can set the environment variables before running Cypress like below:

Linux/OSX

export ELECTRON_EXTRA_LAUNCH_ARGS=--disable-http-cache --lang=es

Windows

set ELECTRON_EXTRA_LAUNCH_ARGS=--disable-http-cache --lang=es

Cypress already sets some the Electron command line switches internally. See file packages/server/lib/environment.js. There is no way to see all currently set switches after Electron's launch.

See all Chrome browser switches

If you are running Cypress tests using a Chromium-based browser, you can see ALL currently set command line switches and the browser version information by opening a new tab and typing chrome://version url.

Examples

Set screen size when running headless

When a browser runs headless, there is no physical display. You can override the default screen size of 1280x720 when running headless as shown below. This will affect the size of screenshots and videos taken during the run.

caution

This setting changes the display size of the screen and does not affect the viewportWidth and viewportHeight set in the Cypress configuration. The viewportWidth and viewportHeight only affect the size of the application under test displayed inside the Cypress Test Runner. Read the blog post Generate High-Resolution Videos and Screenshots for details.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.name === 'chrome' && browser.isHeadless) {
          // fullPage screenshot size is 1400x1200 on non-retina screens
          // and 2800x2400 on retina screens
          launchOptions.args.push('--window-size=1400,1200')

          // force screen to be non-retina (1400x1200 size)
          launchOptions.args.push('--force-device-scale-factor=1')

          // force screen to be retina (2800x2400 size)
          // launchOptions.args.push('--force-device-scale-factor=2')
        }

        if (browser.name === 'electron' && browser.isHeadless) {
          // fullPage screenshot size is 1400x1200
          launchOptions.preferences.width = 1400
          launchOptions.preferences.height = 1200
        }

        if (browser.name === 'firefox' && browser.isHeadless) {
          // menubars take up height on the screen
          // so fullPage screenshot size is 1400x1126
          launchOptions.args.push('--width=1400')
          launchOptions.args.push('--height=1200')
        }

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.name === 'chrome' && browser.isHeadless) {
          // fullPage screenshot size is 1400x1200 on non-retina screens
          // and 2800x2400 on retina screens
          launchOptions.args.push('--window-size=1400,1200')

          // force screen to be non-retina (1400x1200 size)
          launchOptions.args.push('--force-device-scale-factor=1')

          // force screen to be retina (2800x2400 size)
          // launchOptions.args.push('--force-device-scale-factor=2')
        }

        if (browser.name === 'electron' && browser.isHeadless) {
          // fullPage screenshot size is 1400x1200
          launchOptions.preferences.width = 1400
          launchOptions.preferences.height = 1200
        }

        if (browser.name === 'firefox' && browser.isHeadless) {
          // menubars take up height on the screen
          // so fullPage screenshot size is 1400x1126
          launchOptions.args.push('--width=1400')
          launchOptions.args.push('--height=1200')
        }

        return launchOptions
      })
    },
  },
})

Override the device pixel ratio

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.name === 'chrome' && browser.isHeadless) {
          // force screen to behave like retina
          // when running Chrome headless browsers
          // (2560x1440 in size by default)
          launchOptions.args.push('--force-device-scale-factor=2')
        }

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, launchOptions) => {
        if (browser.name === 'chrome' && browser.isHeadless) {
          // force screen to behave like retina
          // when running Chrome headless browsers
          // (2560x1440 in size by default)
          launchOptions.args.push('--force-device-scale-factor=2')
        }

        return launchOptions
      })
    },
  },
})

Start fullscreen

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          launchOptions.args.push('--start-fullscreen')

          return launchOptions
        }

        if (browser.name === 'electron') {
          launchOptions.preferences.fullscreen = true

          return launchOptions
        }
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          launchOptions.args.push('--start-fullscreen')

          return launchOptions
        }

        if (browser.name === 'electron') {
          launchOptions.preferences.fullscreen = true

          return launchOptions
        }
      })
    },
  },
})

Use fake video for webcam testing

By default, Cypress passes the Chrome command line switch to enable a fake video for a media stream. This is to better enable testing webcam functionality without having to have the necessary hardware to test.

You can however send your own video file for testing by passing a Chrome command line switch pointing to a video file.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // Mac/Linux
          launchOptions.args.push(
            '--use-file-for-fake-video-capture=cypress/fixtures/my-video.y4m'
          )

          // Windows
          // launchOptions.args.push('--use-file-for-fake-video-capture=c:\\path\\to\\video\\my-video.y4m')
        }

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'chromium' && browser.name !== 'electron') {
          // Mac/Linux
          launchOptions.args.push(
            '--use-file-for-fake-video-capture=cypress/fixtures/my-video.y4m'
          )

          // Windows
          // launchOptions.args.push('--use-file-for-fake-video-capture=c:\\path\\to\\video\\my-video.y4m')
        }

        return launchOptions
      })
    },
  },
})

Support unique file download mime types

Cypress supports a myriad of mime types when testing file downloads, but in case you have a unique one, you can add support for it.

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, options) => {
        // only Firefox requires all mime types to be listed
        if (browser.family === 'firefox') {
          const existingMimeTypes =
            options.preferences['browser.helperApps.neverAsk.saveToDisk']
          const myMimeType = 'my/mimetype'

          // prevents the browser download prompt
          options.preferences['browser.helperApps.neverAsk.saveToDisk'] =
            `${existingMimeTypes},${myMimeType}`

          return options
        }
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser, options) => {
        // only Firefox requires all mime types to be listed
        if (browser.family === 'firefox') {
          const existingMimeTypes =
            options.preferences['browser.helperApps.neverAsk.saveToDisk']
          const myMimeType = 'my/mimetype'

          // prevents the browser download prompt
          options.preferences['browser.helperApps.neverAsk.saveToDisk'] =
            `${existingMimeTypes},${myMimeType}`

          return options
        }
      })
    },
  },
})

info

Check out our example recipe showing how to download and validate CSV and Excel files.

Disable `--headless=new` for Chrome

Starting in Chrome 112, you can change the value of the --headless flag to the old value before the --headless=new flag was introduced.

on('before:browser:launch', (browser = {}, launchOptions) => {
  if (browser.name === 'chrome' && browser.isHeadless) {
    launchOptions.args = launchOptions.args.map((arg) => {
      if (arg === '--headless=new') {
        return '--headless'
      }

      return arg
    })
  }

  return launchOptions
})

Set a Firefox flag

If we need to set a particular Firefox flag, like browser.send_pings we can do it via preferences

cypress.config.js
cypress.config.ts

const { defineConfig } = require('cypress')

module.exports = defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'firefox') {
          launchOptions.preferences['browser.send_pings'] = true
        }

        return launchOptions
      })
    },
  },
})

import { defineConfig } from 'cypress'

export default defineConfig({
  // setupNodeEvents can be defined in either
  // the e2e or component configuration
  e2e: {
    setupNodeEvents(on, config) {
      on('before:browser:launch', (browser = {}, launchOptions) => {
        if (browser.family === 'firefox') {
          launchOptions.preferences['browser.send_pings'] = true
        }

        return launchOptions
      })
    },
  },
})

History

Version	Changes
4.0.0	New `options` object replaces old `args` as second argument to `before:browser:launch`
4.0.0	All Chromium-based browsers, including Electron, have `chromium` set as their `family` property.
4.0.0	Added `channel` property to browser.

Syntax​

Usage​

Modify browser launch arguments, preferences, extensions, and environment​

Modify browser launch arguments:​

Open devtools by default​

Add browser extensions:​

Configure browser environment:​

Changing browser preferences:​

Modify Electron app switches​

Linux/OSX​

Windows​

See all Chrome browser switches​

Examples​

Set screen size when running headless​

Override the device pixel ratio​

Start fullscreen​

Use fake video for webcam testing​

Support unique file download mime types​

Disable --headless=new for Chrome​

Set a Firefox flag​

History​

Contents

Syntax

Usage

Modify browser launch arguments, preferences, extensions, and environment

Modify browser launch arguments:

Open devtools by default

Add browser extensions:

Configure browser environment:

Changing browser preferences:

Modify Electron app switches

Linux/OSX

Windows

See all Chrome browser switches

Examples

Set screen size when running headless

Override the device pixel ratio

Start fullscreen

Use fake video for webcam testing

Support unique file download mime types

Disable `--headless=new` for Chrome

Set a Firefox flag

History