The Tool Desk
Outbyte Driver Updater FREEScan for outdated or missing drivers - takes under a minuteDriver Scan →Outbyte PC Repair FREERepair Windows errors before they cause bigger problemsFix Now →Call page.setUserAgent() with the options-object form before navigating, then capture the page with page.screenshot(). If you need a mobile-style layout as well as a mobile user-agent, emulate a device before navigation: changing the user-agent alone does not set the viewport.
Set a user-agent before navigating
Install Puppeteer in your project if it is not already available, then use this ES module example. Replace the sample URL and user-agent string with the values for your test.
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import puppeteer from 'puppeteer';
const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.setUserAgent({
userAgent: 'YOUR USER AGENT STRING',
});
await page.goto('https://example.com', { waitUntil: 'networkidle2' });
await page.screenshot({ path: 'screenshot.png' });
} finally {
await browser.close();
}setUserAgent() returns a promise, so await it before goto() when the initial navigation should use that configuration. The screenshot guide demonstrates navigating and then saving an image with page.screenshot({ path: ... }). Its example uses networkidle2, but no single wait condition suits every page; select one that matches the page’s loading behavior. See the Puppeteer user-agent API and screenshot guide.
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The current API accepts an options object with optional userAgent, userAgentMetadata, and platform properties. The older positional form is marked obsolete in the API documentation. Check the documentation matching your installed Puppeteer version; the reviewed API page displayed v25.12.0.
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User-agent override or device emulation?
Choose based on what you need to test. A user-agent string and viewport dimensions are separate settings; changing one does not automatically configure the other.
| Approach | What it configures | Use it when |
|---|---|---|
page.setUserAgent({ userAgent: '…' }) |
The browser’s configured user-agent value; the options object can also include metadata and platform. | You need to test a particular user-agent value and will set any viewport requirements separately. |
page.emulate(device) |
A device profile’s user-agent and viewport. | You want a documented device profile and its associated page dimensions. |
Puppeteer documents page.emulate(device) as a shortcut for setting the user-agent and viewport. Apply it before navigation: viewport changes can affect rendering, and the device-emulation guide notes that many sites do not expect a phone’s size to change after loading. For a custom user-agent, set an appropriate viewport separately if the target layout depends on screen dimensions. See the device-emulation guide.
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Emulate a documented device profile
Import a profile from Puppeteer’s KnownDevices and emulate it before opening the URL:
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import { KnownDevices } from 'puppeteer';
const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
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await page.emulate(device);
await page.goto('https://example.com', { waitUntil: 'networkidle2' });
await page.screenshot({ path: 'mobile.png' });
} finally {
await browser.close();
}Use a profile name available in the KnownDevices list for your installed Puppeteer release. Device emulation is not simply a user-agent override: it also sets viewport dimensions.
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Choose the screenshot output
Save the full page to a file
For a standard image file, pass a path as in the examples. Puppeteer’s screenshot guide also supports capturing an individual element with ElementHandle.screenshot(). It attempts to scroll an element that is out of view into view by default, which is useful when you want a component rather than the whole page.
Use screenshot bytes or base64
The screenshot API’s default result is a Uint8Array. If the surrounding code needs a base64 string, use the API’s base64 encoding option; consult the screenshot API reference for the current option shape and return type.
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Troubleshoot unexpected results
- The first request appears to use the old user-agent: ensure
await page.setUserAgent(...)completes beforepage.goto(). Setting it after navigation cannot change the request that has already occurred. - The site still looks like a desktop page: a user-agent string does not set viewport dimensions. Use
page.emulate(device)before navigation or set a suitable viewport as well. - The page looks unlike a real phone or browser: the documented settings configure user-agent and viewport values, but they do not guarantee that every site will serve the same content it would to a real device. Validate the result on the target site.
- The screenshot is incomplete or times out: review the navigation wait condition for the site’s behavior.
networkidle2is an example, not a universal guarantee that a page’s content is ready. - Your older code uses positional arguments: switch to the options-object form of
setUserAgent(), since the positional form is marked obsolete in the current API documentation.
During a screenshot in a BrowserContext, operations such as creating or closing a page wait for the screenshot operation. page.bringToFront() does not wait for an existing screenshot operation; see the screenshot API reference if coordinating concurrent page work.
Or skip the browser setup
ScreenshotNeo offers a screenshot API and MCP server for developers. One GET request can return an image or PDF; for example, this cURL request saves a WebP screenshot:
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Frequently Asked Questions
Can I change the user-agent after navigating?
You can set it later for subsequent page behavior, but set and await it before navigation when the initial request needs that user-agent.
Does setting a mobile user-agent make Puppeteer render a mobile viewport?
No. Set viewport dimensions separately or use a device profile with page.emulate(device) before navigation.
Will a user-agent override make a site behave exactly as it would on a real device?
Not necessarily. Puppeteer documents the configuration, but does not guarantee identical site behavior; validate against the target site.
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