To change a page’s responsive viewport in Puppeteer, use await page.setViewport({ width, height }), preferably before navigating. To resize the browser window so the page’s content area has specific dimensions, clear the default viewport with await page.setViewport(null) and use page.resize({ contentWidth, contentHeight }). That window-resize method is experimental, so check support in your installed Puppeteer version.
Choose what you need to resize
“Page size” can mean the viewport the site uses for responsive layout, or the browser window’s content area. These are separate controls: setViewport() configures page viewport dimensions; resize() targets the browser window’s content dimensions. The latter is documented as experimental. Puppeteer’s v25.12.0 API documentation covers the viewport method, and its window-management guide shows content sizing.
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Set a responsive viewport
Set the viewport before navigation when possible. Puppeteer notes that some websites do not expect phone-size changes; changing isMobile or hasTouch can also reload the page. The official API example follows this order.
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const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.setViewport({
width: 640,
height: 480,
deviceScaleFactor: 1,
});
await page.goto('https://example.com');
console.log(await page.evaluate(() => ({
width: window.innerWidth,
height: window.innerHeight,
})));
} finally {
await browser.close();
}setViewport() accepts a viewport object or null and returns a promise, so await it. The example uses a 640-by-480 CSS-pixel viewport and a scale factor of 1; change these values to match the layout you want to test.
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Use a device preset when needed
If you need a particular device’s user agent as well as its viewport, use page.emulate(device). Puppeteer describes this as a shortcut for setting both. Emulate before navigation when possible, especially if the site may behave differently when it detects a phone. The cited API result identifies Puppeteer v25.11.0. See the emulate API reference.
Resize the browser window’s content area
Use this approach when the browser window itself must have a chosen content width and height, rather than merely emulating a viewport. The documented sequence removes the default viewport constraint, requests the resize, waits for the browser’s resize event, and then reads the resulting dimensions.
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import puppeteer from 'puppeteer-core';
const browser = await puppeteer.launch({
args: ['--screen-info={800x600}'],
});
try {
const page = (await browser.pages())[0];
// Let the browser window determine the content area size.
await page.setViewport(null);
// Register the listener before requesting the asynchronous resize.
const resized = page.evaluate(() => new Promise(resolve => {
window.addEventListener('resize', resolve, { once: true });
}));
await page.resize({ contentWidth: 600, contentHeight: 400 });
await resized;
const dimensions = await page.evaluate(() => ({
innerWidth: window.innerWidth,
innerHeight: window.innerHeight,
outerWidth: window.outerWidth,
outerHeight: window.outerHeight,
}));
console.log(dimensions);
} finally {
await browser.close();
}The API marks Page.resize experimental, so verify that your installed version and runtime support it before relying on it. Check its API reference. In the official guide’s example environment, the reported inner dimensions are 600×400 and outer dimensions 600×487; the outer size depends on the environment and is not a universal browser-chrome allowance. See the guide.
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Measure the result, not just the setting
page.viewport() returns the last configured viewport or the connection’s defaultViewport; it does not verify the page’s live dimensions. For a window resize, wait for the resize event and inspect browser values such as window.innerWidth and window.innerHeight. The viewport API reference explains what the method reports.
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Unless configured otherwise, ConnectOptions.defaultViewport applies to each page and defaults to 800×600. Setting the viewport to null removes that default viewport constraint in the window-management example. See the ConnectOptions reference.
Keep screen size and screenshot scope separate
Headless Chrome’s screen defaults to 800×600 unless configured with --window-size; --screen-info is headless-only. Headful Chrome uses the platform’s physical screens. Screen geometry is separate from a page’s viewport. Puppeteer’s window-management guide documents these distinctions.
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If the goal is a full-page screenshot, request fullPage: true instead of enlarging the viewport just to capture beyond the visible area. Clipping and capture beyond the viewport are separate screenshot controls. See the screenshot options reference.
Troubleshooting
- The layout did not change: confirm you called and awaited
page.setViewport()on the page you navigate, and that the width and height are the intended viewport dimensions. - The page reloaded after resizing: this can happen when changing
isMobileorhasTouch. Configure those values before navigation where practical. Puppeteer documents this behavior. page.resizeis missing or fails: it is experimental and may not be supported by the installed version or runtime. Check the API reference for the version in use; usesetViewport()instead if you only need responsive rendering.- The measured dimensions seem stale: do not treat
page.viewport()as a live measurement. For window sizing, attach a one-timeresizelistener before callingpage.resize(), then evaluatewindow.innerWidthandwindow.innerHeight. - The outer window dimensions differ from the requested content size:
contentWidthandcontentHeighttarget the content area, not the entire outer window. Browser chrome and runtime environment affect outer measurements. - A full-page screenshot is still cut off: use the screenshot’s
fullPageoption or the relevant clipping controls; viewport resizing alone is not the full-page capture setting.
Or skip the browser setup
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Install the request dependency with python -m pip install requests, then replace the URL and API key:
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import requests
r = requests.get(
"https://api.screenshotneo.com/v1/shot",
params={"access_key": "YOUR_API_KEY", "url": "https://example.com"},
timeout=90,
)
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Frequently Asked Questions
Which Puppeteer version is this guidance based on?
The cited setViewport, window-management, resize, and emulate references identify v25.12.0, except the emulate API result, which identifies v25.11.0. Check the documentation matching your installed version, particularly for experimental methods.
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