Use Cypress to test how a website or web app behaves at deliberately chosen mobile-sized browser viewports: set the size with cy.viewport(), load the page, and assert what a user should see and be able to do. This is responsive mobile web testing—not a simulation of a complete iOS or Android device, and Cypress does not run native mobile apps.
What Cypress mobile viewport testing does—and does not—cover
Cypress changes the application-under-test viewport to specified pixel dimensions or a documented preset. You can also set portrait or landscape orientation. That lets you check responsive layout and behavior in a browser, including whether navigation collapses, content fits, or a menu opens. See the Cypress viewport API documentation.
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Resizing a browser does not reproduce a physical phone. Cypress documents that viewport resizing does not simulate devicePixelRatio. It also does not test native iOS or Android apps: Cypress’s FAQ says, “Cypress will never be able to run on a native mobile app.” Some mobile-like actions, such as swiping, can be mimicked with custom commands, but that is not equivalent to exercising a real touchscreen. See Cypress’s FAQ.
Choose viewport sizes around your app’s breakpoints
Test the sizes that exercise meaningful layout changes rather than every possible resolution. Include at least one size on either side of important responsive breakpoints, and check portrait or landscape when the interface supports both. Cypress’s documentation demonstrates named desktop and phone-sized navigation cases; the dimensions below are illustrative values, not universal device specifications.
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- Small phone: catch cramped layouts, clipped controls, and horizontal overflow.
- Typical phone-sized viewport: verify the primary mobile navigation and actions.
- Tablet-sized viewport: check the transition between phone and desktop layouts.
Replace the example dimensions with values that exercise your CSS breakpoints and the layouts your users need. A viewport dimension is a browser window size, not a guarantee of how a particular handset will render the page.
Write an end-to-end responsive navigation test
This example runs a separate test for each size, visits the application, and checks both visibility and interaction. Replace the route and selectors with your app’s route and stable test hooks.
const sizes = [
{ name: 'small phone', width: 320, height: 568 },
{ name: 'phone', width: 375, height: 812 },
{ name: 'tablet', width: 768, height: 1024 },
]
describe('responsive navigation', () => {
for (const size of sizes) {
it(`works at ${size.name}`, () => {
cy.viewport(size.width, size.height)
cy.visit('/')
cy.get('[data-testid="desktop-nav"]').should('not.be.visible')
cy.get('[data-testid="mobile-menu-button"]')
.should('be.visible')
.click()
cy.get('[data-testid="mobile-nav"]').should('be.visible')
})
}
})The viewport call belongs before the page visit so the page loads at the intended size. Assertions should describe user-visible outcomes, not merely the existence of DOM nodes. For example, verify that a menu button is visible and opens the mobile navigation; add checks for closing the menu, following a link, or dismissing it if those behaviors matter to your interface.
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Set viewport sizes in Cypress configuration or in a test
Cypress’s documented default application viewport is 1000 × 660 pixels. You can set global defaults, set viewport values for a test or suite, or use cy.viewport() when a test needs to change size. Cypress automatically restores the default viewport size between tests.
Set a global default
In the Cypress configuration file, set viewportWidth and viewportHeight for your project. This is useful when most tests should start from the same viewport; individual tests can still use cy.viewport() for responsive cases.
import { defineConfig } from 'cypress'
export default defineConfig({
e2e: {
viewportWidth: 375,
viewportHeight: 812,
},
})Configuration format can depend on your project setup. See Cypress configuration documentation.
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Set the viewport for a particular test
Use test configuration when a test or suite has a known viewport requirement. Use cy.viewport() when the size is selected dynamically or you want to iterate over several sizes within a test workflow.
Since Cypress 16.0.0, changing viewportWidth or viewportHeight through Cypress.config() during test execution throws an error. Use test configuration or cy.viewport() instead. See the Cypress.config() API documentation.
Cover the mobile outcomes users rely on
Use behavior-focused assertions at each selected viewport. A responsive test suite is more useful when it covers the key changes in your interface than when it merely repeats the same page load at many dimensions.
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- Navigation: check which navigation is shown, whether the mobile menu opens and closes, and whether its links work.
- Content and layout: check important text and controls remain visible, content wraps as intended, and the page does not acquire unwanted horizontal overflow.
- Forms and primary actions: verify controls can be reached and used, validation messages appear, and submission reaches the expected state.
- Menus and dialogs: check that overlays fit the viewport and can be dismissed using the supported controls.
- Touch-like interactions: test the actual behavior your web app implements. Custom commands can mimic actions such as swiping, but do not treat them as physical-device touch validation.
Use component tests when layout isolation helps
For an individual responsive component, Cypress component testing mounts it in a real browser, which can make it easier to isolate layout and interaction behavior. End-to-end tests remain useful for checking the complete app, including routing and integrated page behavior. See Cypress component testing documentation.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Add visual checks without confusing them with behavior tests
Functional assertions establish that controls and responsive states behave as expected. Screenshot comparison can catch visual defects those assertions may miss, such as a misaligned element or a change in wrapping. For useful comparisons, keep the rendering conditions consistent: viewport dimensions and orientation, browser version, operating system, display scaling, and font environment can all affect screenshots. Cypress explains these considerations in its visual testing guide.
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Choose whether a check is functional or screenshot-based, and keep its environment stable. A visual match in one browser setup does not prove that every device or operating system renders identically.
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Troubleshoot common viewport-test failures
- The wrong navigation appears: confirm the viewport is set before visiting the page, and check that the chosen dimensions actually cross the breakpoint in your CSS.
- A hidden element passes a presence check: assert visibility or the relevant user outcome rather than only querying whether the element exists.
- The test changes size through
Cypress.config()and errors: on Cypress 16.0.0 and later, usecy.viewport()or test configuration for viewport changes. - A page does not load during
cy.visit(): check that the route is reachable and that the app has loaded as expected. Cypress’s cy.visit() documentation describes navigation and load behavior. - A screenshot differs between runs or machines: fix the viewport and keep browser, operating system, display scaling, and fonts consistent before treating the difference as an app regression.
- A test is being treated as proof of phone behavior: remember that viewport resizing does not emulate device pixel ratio or native hardware. Validate on actual target devices when those characteristics are material.
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