Use cy.viewport(width, height) to set a viewport during a test, or set viewportWidth and viewportHeight in Cypress configuration for project defaults. For example, cy.viewport(1280, 720) switches the application under test to a 1280 × 720 viewport.
Set the viewport inside a test
Call cy.viewport() in the test at the point where you want the app to render at a different size. Cypress supports exact dimensions or a named preset:
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describe('responsive layout', () => {
it('shows the desktop navigation at 1280 × 720', () => {
cy.viewport(1280, 720);
cy.visit('/');
cy.get('[data-testid="desktop-navigation"]').should('be.visible');
});
it('uses the iPhone 6 portrait preset', () => {
cy.viewport('iphone-6');
cy.visit('/');
cy.get('[data-testid="mobile-menu"]').should('be.visible');
});
});The documented command forms are cy.viewport(width, height) and cy.viewport(preset, orientation). Both can also take an options object. The command is chained from cy, yields null, and is not itself a value to assert on. Numeric dimensions must be finite, non-negative numbers. See the Cypress viewport API reference for the current command signature.
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Use numeric dimensions when your test needs a specific breakpoint or an exact repeatable canvas. Presets are a convenient shorthand when a documented device-like viewport is sufficient. The API currently documents these preset dimensions:
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| Preset | Dimensions |
|---|---|
ipad-2, ipad-mini |
768 × 1024 |
iphone-3, iphone-4 |
320 × 480 |
iphone-5 |
320 × 568 |
iphone-6, iphone-7, iphone-8, iphone-se2 |
375 × 667 |
iphone-6+ |
414 × 736 |
iphone-x |
375 × 812 |
iphone-xr |
414 × 896 |
macbook-11 |
1366 × 768 |
macbook-13 |
1280 × 800 |
macbook-15 |
1440 × 900 |
macbook-16 |
1536 × 960 |
samsung-note9 |
414 × 846 |
samsung-s10 |
360 × 760 |
Preset names and dimensions are API details that may change; check the current reference before relying on a particular one. Orientation defaults to portrait. Pass 'landscape' to reverse a preset’s width and height:
cy.viewport('iphone-6', 'landscape');Set project-wide default dimensions
For a default that applies across your project, set viewportWidth and viewportHeight in Cypress configuration. Cypress documents default dimensions of 1000 × 660 pixels.
import { defineConfig } from 'cypress';
export default defineConfig({
e2e: {
viewportWidth: 1280,
viewportHeight: 720,
},
});Use the configuration file for project defaults rather than repeating the same cy.viewport() call in every test. The configuration reference documents the available configuration locations and precedence: Cypress configuration.
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Override dimensions from the command line or environment
For a one-off run with different dimensions, pass configuration values to Cypress:
npx cypress run --config viewportWidth=1280,viewportHeight=720You can also override them with the environment variables CYPRESS_VIEWPORT_WIDTH and CYPRESS_VIEWPORT_HEIGHT.
Scope dimensions to a suite or test
When only a particular suite or test needs another viewport, use test-specific configuration rather than changing the project default. Cypress restores the prior/default viewport dimensions after the scoped test configuration ends.
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describe('mobile layout', { viewportWidth: 375, viewportHeight: 667 }, () => {
it('shows the mobile navigation', () => {
cy.visit('/');
cy.get('[data-testid="mobile-menu"]').should('be.visible');
});
});
it('checks one tablet-sized view', { viewportWidth: 768, viewportHeight: 1024 }, () => {
cy.visit('/');
cy.get('[data-testid="tablet-layout"]').should('be.visible');
});Use this scope when the dimensions belong to the test’s setup, not as a mid-test transition. For a test that deliberately changes size as it runs, call cy.viewport() at each transition.
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The viewport is the size Cypress uses for the application under test. In the Cypress app, the runner may scale and center that application preview to fit the available window; this visual zoom does not change the app’s viewport calculations or behavior. A preview that looks smaller on screen does not mean the test is using smaller CSS viewport dimensions. See Cypress open mode.
What viewport emulation does—and does not—test
A preset gives your web app a viewport size and orientation; it does not reproduce every property of a physical phone. Cypress documents that devicePixelRatio is not simulated. Viewport checks are useful for responsive mobile-web layouts, but they are not native mobile-app tests. Cypress says it cannot run native mobile apps, while it can control mobile-web viewports; its FAQ addresses the distinction.
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Make responsive and visual checks repeatable
For screenshot-based visual checks, keep the viewport fixed and generate and compare screenshots in the same environment. Viewport dimensions are one controlled comparison condition; changing them between baseline and comparison can change wrapping, breakpoints, and page height independently of a UI change. Cypress’s guidance is in Visual testing in Cypress.
- Choose explicit width and height for breakpoint tests, rather than relying on the runner window size.
- Keep the viewport consistent between the screenshot used as a baseline and the screenshot under comparison.
- When testing portrait and landscape, define them as separate cases so the expected layout is clear.
Troubleshooting viewport issues
Cypress.config() throws when changing viewport dimensions
Since Cypress 16.0.0, changing viewportWidth or viewportHeight through Cypress.config() while a test is executing throws an error. That change would affect the next test, rather than resizing the running test. Use cy.viewport(width, height) for an in-test change, or set dimensions in suite- or test-specific configuration. See the viewport API and configuration reference.
The app appears small in the Cypress runner
Check the runner’s preview scaling before changing test dimensions. Cypress can scale the preview to fit the runner window without changing the viewport the app uses. Use explicit viewport dimensions in the test when the behavior depends on a particular size.
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A preset name or dimensions do not match expectations
Confirm that the preset exists in the current viewport API reference and verify its documented dimensions. Preset names and values are versioned API details. If the exact width and height matter, use numeric dimensions instead.
A mobile viewport does not reproduce a physical phone
Viewport size and orientation alone do not simulate devicePixelRatio or native-app behavior. Treat the test as a responsive web check, not a complete device simulation.
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Frequently Asked Questions
Does Cypress reset the viewport between tests?
Yes. Cypress resets the viewport to its default size between tests; scoped test configuration returns to the prior/default dimensions afterward.
Can I use Cypress viewport presets to test a native mobile app?
No. Cypress viewport controls apply to web content and do not make Cypress a native mobile-app test runner.
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