Custom Browser Fingerprints: Control the Signals Sites Read

TL;DR:

• A browser fingerprint is the set of signals a site reads to identify your browser — user agent, platform, screen, timezone, language, canvas and WebGL. When they disagree with each other, automation gets flagged.
• Scrapeless Scraping Browser lets you set the fingerprint explicitly. Pass a fingerprint object and the cloud browser reports exactly those values, kept internally consistent.
• The override is real, not cosmetic. In a live run, navigator.userAgent, navigator.platform (Win32), the resolved timezone (Asia/Hong_Kong), and navigator.language all came back as the values set — verified below.
• Consistency is the point. A US user agent with a Hong Kong timezone and a datacenter IP is the mismatch anti-bot systems look for; set the fingerprint and egress to tell one coherent story.
• It rides on a standard Puppeteer connection. The fingerprint is a query parameter on the WebSocket endpoint; your navigation code is unchanged.
• Free to start. New Scrapeless accounts include free Scraping Browser runtime — sign up at app.scrapeless.com.

Introduction: the browser is telling on you

Every page you load reads a set of signals to decide what kind of client you are: the user agent string, the platform, the screen size, the language and timezone, and deeper values like the canvas and WebGL fingerprint. A real browser reports these consistently — a US-configured Chrome on Windows has a US-ish timezone, a matching platform, and a normal screen. Automation tends to leak a different story: a headless default here, a mismatched timezone there, a navigator.webdriver flag that no human browser sets.

Scrapeless Scraping Browser lets you set that story on purpose. You pass a fingerprint object when you open the session, and the cloud browser reports exactly those values — coherently, so the signals agree with each other. This guide covers the fingerprint fields, how to set them over a standard Puppeteer connection, and a live check that the override actually takes effect.

What you can control

• User agent — the full UA string the browser reports.
• Platform — Windows, macOS, or Linux, reflected in navigator.platform.
• Screen — the reported width and height.
• Localization — the timezone and the ordered list of languages.
• Launch args — Chromium flags such as window size.

The values are kept internally consistent, so the browser doesn't report a Windows platform with a macOS user agent.

Why Scrapeless Scraping Browser

Scrapeless Scraping Browser is a customizable, anti-detection cloud browser designed for web crawlers and AI agents. For fingerprint control specifically, it brings:

• Explicit fingerprint fields — user agent, platform, screen, timezone, and languages set per session.
• Internal consistency — no navigator.webdriver tell, and the values you set agree with each other.
• Residential proxies in 195+ countries — pair the fingerprint's region with matching egress so the two signals line up.
• A standard Puppeteer connection — puppeteer.connect() returns an ordinary Browser; the fingerprint is set on the endpoint URL.

Get your API key on the free plan at app.scrapeless.com.

Prerequisites

• Node.js 18 or newer
• A Scrapeless account and API key — sign up at app.scrapeless.com
• Basic familiarity with Puppeteer

Install

npm install puppeteer-core

export SCRAPELESS_API_KEY="your_api_token_here"

Setting a fingerprint

Build the fingerprint object, URL-encode it, and pass it as the fingerprint query parameter on the WebSocket endpoint. Everything else is a normal Puppeteer session:

import puppeteer from 'puppeteer-core';

const fingerprint = {
  userAgent:
    'Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/134.0.0.0 Safari/537.36',
  platform: 'Windows',
  screen: { width: 1280, height: 1024 },
  localization: { languages: ['en-US', 'en'], timezone: 'Asia/Hong_Kong' },
  args: { '--window-size': '1280,1024' },
};

const params = new URLSearchParams({
  token: process.env.SCRAPELESS_API_KEY,
  sessionTTL: '180',
  proxyCountry: 'ANY',
  fingerprint: encodeURIComponent(JSON.stringify(fingerprint)),
});

const browser = await puppeteer.connect({
  browserWSEndpoint: `wss://browser.scrapeless.com/api/v2/browser?${params}`,
});
const page = await browser.newPage();
await page.goto('https://example.com', { waitUntil: 'domcontentloaded' });
await browser.close();

Confirming the override took effect

Read the signals back from inside the page to confirm they match what you set:

const reported = await page.evaluate(() => ({
  userAgent: navigator.userAgent,
  platform: navigator.platform,
  timezone: Intl.DateTimeFormat().resolvedOptions().timeZone,
  language: navigator.language,
}));
console.log(reported);
// {
//   userAgent: "Mozilla/5.0 (Windows NT 10.0; Win64; x64) … Chrome/134.0.0.0 Safari/537.36",
//   platform: "Win32",
//   timezone: "Asia/Hong_Kong",
//   language: "en-US"
// }

In a live run, all four came back as the fingerprint's values — the user agent verbatim, platform as Win32 (from platform: 'Windows'), the resolved timezone as Asia/Hong_Kong, and the language as en-US. The override reaches the JavaScript environment the page actually reads, not just the request header.

Get your API key on the free plan: app.scrapeless.com

Make the signals agree

A fingerprint helps only when its parts tell one story. The common mismatches that get a session flagged:

• Timezone vs. IP — a Hong Kong timezone behind US egress reads as inconsistent. Set proxyCountry to a region that matches the timezone and languages, or set the timezone to match the egress. Timezone handling follows the IANA zones referenced by the Intl.DateTimeFormat API.
• Platform vs. user agent — a Windows platform with a macOS UA string is a contradiction. Keep the platform field and the UA's OS token aligned; the UA grammar is defined in the HTTP semantics specification.
• Language vs. region — order languages the way a user in that region would, with the primary locale first.
• Screen vs. window — keep the screen dimensions and the --window-size arg sensible for the device you're impersonating.

These signals are exactly the kind of automated-client tells catalogued in the OWASP Automated Threats project — coherence across them is what a real browser has and a careless bot doesn't.

Advanced patterns

Rotate fingerprints across sessions, not within one. Keep a fingerprint stable for the life of a session so the story doesn't change mid-visit; vary it between sessions instead.

Pin egress to the fingerprint's region. Set proxyCountry (and proxyState/proxyCity when needed) to match the timezone and languages you chose.

Persist an identity with a profile. When you need the same identity across runs, pair the fingerprint with a browser profile so cookies and storage carry over.

Keep it plausible. A fingerprint that no real device would produce is as suspicious as a default one — use values that describe a browser that actually exists.

Conclusion: one coherent identity

A custom fingerprint is not a single trick — it's the difference between a browser that reports one consistent identity and one that contradicts itself. Set the user agent, platform, screen, timezone, and languages together, pin egress to match, and the values a site reads agree the way a real browser's do. Pair it with the Scraping Browser session controls and residential egress, read up on why IP reputation matters, and the docs cover every field.

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FAQ

Q: What is a browser fingerprint?
The set of signals a site reads to identify your browser — user agent, platform, screen size, timezone, language, and deeper values like canvas and WebGL. Sites combine them into an identifier and flag combinations that don't look like a real device.

Q: Does setting the fingerprint actually change what the page sees?
Yes. In a live run, navigator.userAgent, navigator.platform, the resolved timezone, and navigator.language all returned the values set on the session — the override reaches the JavaScript environment, not just the request header.

Q: Should the timezone match the proxy country?
Yes. A timezone that contradicts the exit IP's region is a common flag. Set proxyCountry to match the fingerprint's timezone and languages, or set the timezone to match the egress.

Q: Can I rotate fingerprints?
Rotate between sessions, not within one. A fingerprint that changes mid-session is itself a signal; keep it stable per session and vary it across sessions.

Q: Do I need an AI agent or SDK for this?
No. The fingerprint is a query parameter on the standard Puppeteer WebSocket endpoint — plain puppeteer.connect(), no agent required.