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The safest default is to establish the viewport before navigation, especially when testing a phone-sized layout. The browser context default is 1280×720 when you do not provide a viewport.
Choose the right viewport scope
Viewport configuration is hierarchical. Pick the narrowest scope that expresses your intent; a shared context or test configuration prevents accidental differences between pages.
| Need | Use | What it affects |
|---|---|---|
| Resize one page, including during a test | page.setViewportSize({ width, height }) |
That page only; the call also resets its emulated screen size. |
| Give all pages in a context the same dimensions | browser.newContext({ viewport: { width, height } }) |
Every page created by that context. |
| Apply a standard size to tests or a project | use.viewport or test.use() |
Playwright Test projects, files, describe blocks, or individual tests. |
| Emulate a named phone or desktop | ...devices['Device name'] |
Viewport plus user agent, touch capability, screen characteristics, and other device settings. |
| Record a script at a fixed size | npx playwright codegen --viewport-size="W,H" URL |
The code generator’s browser window. |
Set a viewport on one page
Use the Page API when only one page needs a different layout, or when a test intentionally changes size partway through.
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import { chromium } from 'playwright';
const browser = await chromium.launch();
const page = await browser.newPage();
await page.setViewportSize({ width: 640, height: 480 });
await page.goto('https://example.com');
console.log(await page.title());
await browser.close();Put setViewportSize before goto whenever the initial responsive state matters. Many sites do not expect a phone-sized page to change after loading; navigating at the final dimensions lets CSS, JavaScript, and responsive breakpoints initialize consistently.
Resize an existing page
await page.goto('https://example.com');
await page.setViewportSize({ width: 1440, height: 900 });
// Future layout and screenshots use the new viewport.Changing the viewport does not recreate the page or context. It changes the page dimensions and resets the emulated screen size. If your test needs independent control of window.screen, configure both viewport and screen when creating the context instead.
Set a context default
A browser context is the practical choice for a suite that opens several pages with one consistent viewport. Supply the option to browser.newContext() before creating any pages.
import { chromium } from 'playwright';
const browser = await chromium.launch();
const context = await browser.newContext({
viewport: { width: 1280, height: 1024 },
});
const page = await context.newPage();
await page.goto('https://example.com');
const secondPage = await context.newPage();
await secondPage.goto('https://example.com/pricing');
await context.close();
await browser.close();If no viewport is supplied, Playwright documents a 1280×720 default. Explicit values make the test’s rendering independent of the machine running it.
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Control screen dimensions separately
viewport controls the page’s layout viewport. The context’s screen option emulates window.screen and is used when a viewport is set.
const context = await browser.newContext({
viewport: { width: 1280, height: 800 },
screen: { width: 1440, height: 900 },
});Use this distinction only when application code reads screen properties. For ordinary responsive testing, a viewport alone is simpler and less error-prone.
Configure Playwright Test
When many tests share dimensions, put the setting in the test runner rather than repeating page setup.
Global or project-level configuration
import { defineConfig } from '@playwright/test';
export default defineConfig({
use: {
viewport: { width: 1280, height: 720 },
},
});For separate desktop and mobile runs, define projects with different use.viewport values. This keeps each worker’s environment consistent and makes the chosen dimensions visible in the configuration.
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Override a file, describe block, or test
import { test, expect } from '@playwright/test';
test.use({ viewport: { width: 1600, height: 1200 } });
test('wide layout', async ({ page }) => {
await page.goto('https://example.com');
await expect(page.locator('nav')).toBeVisible();
});
test.describe('tablet checks', () => {
test.use({ viewport: { width: 1024, height: 768 } });
test('tablet layout', async ({ page }) => {
await page.goto('https://example.com');
});
});test.use() can scope settings to the remaining tests in a file or to a describe block. Keep the dimensions near the tests that need them so a later change does not silently alter unrelated coverage.
Combine a custom viewport with a device preset
A device descriptor is more than a width and height. It can include a mobile user agent, screen size, touch support, and other emulation behavior. Use one when those characteristics affect the code under test; use a custom viewport when dimensions are the only variable.
import { defineConfig, devices } from '@playwright/test';
export default defineConfig({
projects: [
{
name: 'chromium-custom-width',
use: {
...devices['Desktop Chrome'],
viewport: { width: 1280, height: 720 },
},
},
],
});The order matters: put your explicit viewport after the spread. The device descriptor contains its own viewport, so placing your value first would allow the preset to overwrite it.
Viewport dimensions alone do not turn a desktop browser into a real handset. Full device emulation has browser-specific limits; for example, the Browser API documents that isMobile is not supported in Firefox.
Set device scale factor when pixel density matters
Viewport width and height are CSS-pixel dimensions. A separate deviceScaleFactor controls the emulated device pixel ratio, which affects rasterization and screenshots without changing the CSS viewport.
const context = await browser.newContext({
viewport: { width: 2560, height: 1440 },
deviceScaleFactor: 2,
});Use this for high-DPI rendering checks or when an image comparison must represent a particular pixel density. Do not use scale factor as a substitute for changing responsive breakpoints.
Use a fixed size with codegen
To record interactions at a chosen viewport, pass width and height as a comma-separated value:
npx playwright codegen --viewport-size="800,600" https://playwright.devIf you need the broader behavior of a named device while recording, use codegen’s --device option instead of only setting dimensions.
Build a repeatable viewport matrix
Responsive bugs usually appear at breakpoints rather than at one arbitrary size. Define a small, intentional matrix and run the same assertions at each size.
import { test, expect } from '@playwright/test';
const viewports = [
{ name: 'phone', width: 390, height: 844 },
{ name: 'tablet', width: 768, height: 1024 },
{ name: 'desktop', width: 1440, height: 900 },
];
for (const viewport of viewports) {
test(`${viewport.name} navigation`, async ({ browser }) => {
const context = await browser.newContext({
viewport: { width: viewport.width, height: viewport.height },
});
const page = await context.newPage();
await page.goto('https://example.com');
await expect(page.locator('body')).toBeVisible();
await context.close();
});
}Keep the list small enough to run on every change, and add dimensions only when they represent a product breakpoint or a known failure. Reusing a context for pages that share a size avoids repeated setup; create separate contexts when isolation or different emulation is required.
Why viewport: null is usually the wrong choice
Setting viewport: null opts out of consistent viewport emulation and lets the host window determine the size. The documented result is nondeterministic test execution: a laptop, CI worker, and headed browser can render different layouts.
Use explicit width and height for visual assertions, responsive branching, and screenshot comparison. Reserve null for a deliberate test of host-window behavior, and record the environment if you choose it.
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When a layout assertion fails, print the values exposed to page scripts before changing configuration.
const dimensions = await page.evaluate(() => ({
innerWidth: window.innerWidth,
innerHeight: window.innerHeight,
screenWidth: window.screen.width,
screenHeight: window.screen.height,
devicePixelRatio: window.devicePixelRatio,
}));
console.log(dimensions);innerWidth and innerHeight show the CSS viewport. The screen values reveal whether a separate screen option or a device preset is influencing the page, and devicePixelRatio confirms scale-factor behavior.
Troubleshooting viewport problems
The first render uses the wrong breakpoint
Cause: the page was navigated before the final viewport was applied.
Fix: set the viewport in newContext, in Playwright Test configuration, or call setViewportSize before goto. If you resize after navigation intentionally, wait for the responsive UI to settle before asserting.
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My explicit size is ignored when using a device
Cause: the device descriptor was spread after your custom value.
Fix: spread the descriptor first and put viewport: { width, height } afterward.
Assertions pass locally but fail in CI
Cause: a missing viewport or viewport: null allows the host window to decide the dimensions.
Fix: define explicit dimensions in the context or use configuration, and log the evaluated dimensions when diagnosing a failure.
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CSS responds correctly but JavaScript reads unexpected screen values
Cause: viewport and screen are separate emulated properties.
Fix: provide a context-level screen value when the application depends on window.screen. A later page resize also resets screen size.
A phone test behaves like desktop
Cause: only the viewport was changed; user agent, touch, and other device behavior remain desktop-like.
Fix: start from an appropriate devices preset and override its viewport only if you need nonstandard dimensions. Check browser support for each emulation option.
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Screenshots have the wrong pixel density
Cause: CSS dimensions were correct but the device scale factor was not.
Fix: set deviceScaleFactor at context creation and keep it separate from viewport width and height.
Or skip the browser setup
If your goal is a clean image or PDF of a URL rather than an interactive Playwright test, ScreenshotNeo provides a single GET request. It can capture a full page, load lazy images, select one element, apply a viewport or device preset, use retina scale, wait for a selector, delay, or network idle, and return PNG, JPEG, WebP, or PDF output. You can also supply custom CSS or JavaScript, headers, cookies, user-agent, timezone, geolocation, blocking rules, caching, signed links, asynchronous webhooks, and bulk requests.
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Use the API examples below with an access key; the parameter names used by many other screenshot APIs are accepted, which can simplify a migration. Full parameter details are in the ScreenshotNeo documentation.
cURL
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://playwright.dev -o shot.webpPython
import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://playwright.dev"},
timeout=90,
)
r.raise_for_status()
open("shot.webp", "wb").write(r.content)Node.js
const q = new URLSearchParams({
access_key: 'YOUR_API_KEY',
url: 'https://playwright.dev',
});
const res = await fetch(`https://api.screenshotneo.com/v1/shot?${q}`);
if (!res.ok) throw new Error(`Screenshot failed: ${res.status}`);
const fs = await import('node:fs/promises');
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FAQ
Can I change a viewport more than once in one test?
Yes. Call page.setViewportSize() again for the same page, then wait for any application-specific responsive transition before taking measurements or screenshots.
Does viewport width include the browser’s outer window or scrollbars?
Playwright’s values describe the emulated page viewport in CSS pixels, not the operating-system window frame. Validate the value your page receives with window.innerWidth when an application has unusual scrollbar behavior.
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Use the smallest matrix that covers your supported breakpoints. A single size is faster, while a few named phone, tablet, and desktop sizes catch layout changes that occur between breakpoints.
Frequently Asked Questions
Can I change a viewport more than once in one test?
Yes. Call page.setViewportSize() again for the same page, then wait for any application-specific responsive transition before taking measurements or screenshots.
Does viewport width include the browser’s outer window or scrollbars?
Playwright’s values describe the emulated page viewport in CSS pixels, not the operating-system window frame. Validate the value your page receives with window.innerWidth when an application has unusual scrollbar behavior.
Should visual regression tests use one viewport or several?
Use the smallest matrix that covers your supported breakpoints. A single size is faster, while a few named phone, tablet, and desktop sizes catch layout changes that occur between breakpoints.
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