Set the custom User-Agent on the browser session before it opens the page, then navigate and capture the page with that browser’s screenshot API. With Playwright, configure userAgent on a browser context; with Puppeteer, call page.setUserAgent() before navigation. An AI agent can use this workflow only if its browser-control tool exposes those settings—or if it can run the automation code—and the resulting image must be passed to the model by the agent integration.
What the custom User-Agent does—and what it does not
A User-Agent string tells a site which browser identity to present for the request. It can help you inspect how a site responds to a different browser identity, but it is only one part of a browser or device profile. Viewport, screen size, touch support and other emulated properties are separate settings; changing the string alone does not make a desktop browser equivalent to a physical phone. Playwright documents the User-Agent override and other emulation properties separately in its emulation guide.
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Set the override before navigation so the page loads under the intended configuration. A site may ignore, vary, or block a particular User-Agent; the code cannot guarantee a specific site response.
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This JavaScript example creates a Chromium context with a custom User-Agent and viewport, opens a page, waits for DOM content, and saves a full-page PNG:
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import { chromium } from 'playwright';
const browser = await chromium.launch();
try {
const context = await browser.newContext({
userAgent: 'Example custom user agent string',
viewport: { width: 1280, height: 800 },
});
const page = await context.newPage();
await page.goto('https://example.com', { waitUntil: 'domcontentloaded' });
await page.screenshot({ path: 'page.png', fullPage: true });
} finally {
await browser.close();
}Install Playwright and its browser runtime in the environment where the script will run. Replace the example User-Agent and URL with the values appropriate to your test. The userAgent context option is documented in Playwright emulation, while navigation and screenshot methods are documented in the Page API.
Choose the screenshot area
- Viewport: omit
fullPageor set it tofalseto capture the visible viewport. - Full page: use
fullPage: trueto capture content beyond the visible viewport. - One element: locate the element and call its screenshot method, for example
await page.locator('main').screenshot({ path: 'main.png' });. Choose a selector that uniquely identifies the intended region.
Playwright’s screenshot tool reference describes screenshot target, full-page, output type, filename, and scale controls for its MCP tooling.
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Wait for the state you need
domcontentloaded waits for the initial document to be parsed; it does not ensure that every image, font, or client-rendered component is ready. If the relevant content appears later, wait for a specific selector, or use a page-appropriate load condition. A fixed delay can be useful for a known animation or delayed update, but it is less reliable than waiting for the state your task requires. Pages with persistent network activity may never reach a network-idle condition, so select waits based on the page rather than assuming one condition fits all.
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Make the browser profile match the question
If you are checking a mobile layout, pair the User-Agent with a mobile-sized viewport and any other device properties the test requires. A desktop-sized viewport with a mobile User-Agent may produce a mixed configuration: the site sees one identity while the browser lays out a much larger screen. Playwright provides device emulation options in addition to the User-Agent setting; use a consistent profile when the distinction matters, and verify the rendered result rather than treating the string as proof of a device.
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For a targeted visual check, decide whether you need the viewport, a specific element, or the full scrollable page before capture. Larger full-page images can be harder for an agent to inspect and may include irrelevant sections; element captures narrow the view but can omit surrounding context.
Give the screenshot to the AI agent
Capturing an image and giving it to a model are separate operations. The browser automation produces a file or image result; the agent’s integration must then make that image available to the model. A browser agent may already provide a screenshot tool, in which case configure its supported User-Agent and capture options. Otherwise, run Playwright from a tool the agent can call and expose the saved image to the agent.
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Use the screenshot for visual questions such as layout, chart appearance, clipping, or documenting a defect. If the agent needs text, element identity, or reliable interaction targets, pair the image with a structured accessibility or DOM-facing representation. Playwright’s Page API documents accessibility-oriented snapshots and references; its screenshot guidance distinguishes visual inspection from page structure and interactions.
Puppeteer alternative
Puppeteer applies the override on a page rather than through Playwright’s context option. Set it before navigating:
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const browser = await puppeteer.launch();
try {
const page = await browser.newPage();
await page.setUserAgent('Example custom user agent string');
await page.goto('https://example.com', { waitUntil: 'networkidle2' });
await page.screenshot({ path: 'page.png', fullPage: true });
} finally {
await browser.close();
}Puppeteer’s User-Agent API documents Page.setUserAgent(), and its screenshot guide covers page and element screenshots. The example uses networkidle2; pages that keep requests open may not satisfy that wait condition, so use a more appropriate wait for the target page when necessary. Playwright and Puppeteer use different APIs; do not mix their configuration calls.
Or skip the browser setup
ScreenshotNeo is a website screenshot API and MCP server. For a direct API call, send a URL and save the returned image:
curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://example.com -o shot.webpSee the ScreenshotNeo documentation for API options, including the custom User-Agent parameter. ScreenshotNeo also provides an MCP server with screenshot tools for AI agents. Before capture, it accepts cookie or consent banners like a visitor and removes more than 60 known consent platforms, newsletter popups, and chat widgets; each of those steps can be turned off. Bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and response headers report the page verdict and billing status.
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Troubleshooting
- The page still looks like the default browser: confirm the custom string was set on the context or page before navigation, then reload the page in that session.
- The layout does not look like a phone: User-Agent is not a complete device profile. Set a matching viewport and the relevant emulation properties, then capture again.
- The screenshot is blank or missing late content: the page may not have finished rendering when capture ran. Wait for the content selector or another page-specific state before taking the screenshot.
- The script hangs while waiting for network idle: the site may keep network requests open. Use a selector or another suitable readiness condition instead.
- The capture omits the area you wanted: choose full-page capture for below-the-fold content, or capture a specific element for a focused region.
- The agent cannot interpret the saved image: check whether its tool integration passes the image to the model. For text or interaction tasks, supply a structured accessibility or DOM-facing snapshot as well.
Frequently Asked Questions
Does changing the User-Agent guarantee that a website will show a different version?
No. The override changes the browser identity sent by the automation session, but the site decides how to respond and may ignore or block it.
Can an AI model change the browser User-Agent by itself?
Not unless the agent has a browser-control tool or can run automation code that exposes the setting.
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