What Is a Browser Fingerprint?

A browser fingerprint is an identifier built from many small facts about your browser and device, none of which identifies you alone. MDN defines fingerprinting as a practice in which websites "identify a particular browser (and by extension, a particular user) by collecting and combining distinguishing features of the browser and underlying operating system" (MDN: Fingerprinting). The same idea is called device fingerprinting when the profile leans on hardware signals, or a digital fingerprint in general.

The W3C splits it into two kinds (W3C: Mitigating Browser Fingerprinting in Web Specifications, Group Note of 25 September 2025):

• Passive fingerprinting uses what is visible in the request itself: the IP address, the User-Agent and other HTTP headers, and the TLS handshake. No code runs on your device.
• Active fingerprinting runs JavaScript on the page to read more: screen size, fonts, canvas and WebGL output, audio processing, hardware details. Your browser could, in principle, notice it.

A site rarely needs every signal. A dozen ordinary values, combined, can be rare enough to pick one browser out of many.

A fingerprint combines request data, browser settings and the output of your hardware. The table lists the common signals and how a site reads them.

MDN lists the same core: the browser version, the time zone and preferred language, the available video and audio codecs, installed fonts, the state of browser settings and the display size (MDN). The TLS part works below the browser's scripts; see TLS and TCP fingerprinting.

Browser fingerprinting works in four steps: collect, combine, store and match.

Fingerprints drift as browsers update, so serious systems match on similarity rather than one exact hash, and they weigh stable signals (the GPU, fonts) more than volatile ones (the browser's minor version).

A cookie is a file the site stores in your browser; a fingerprint is computed from what your browser is, so there is nothing to delete.

The EFF's Cover Your Tracks explains why this matters: cookies can be deleted, while fingerprints rely on "more permanent identifiers such as hardware specifications and browser settings" (EFF: Cover Your Tracks, Learn). The W3C note also describes fingerprints used like "super" cookies, to restore an identity after you clear your cookies.

Websites use browser fingerprinting for four jobs, and only one of them is advertising.

• Fraud prevention. Banks and shops flag a login or payment from a device they have never seen with that account.
• Bot detection. Anti-bot systems check whether a "Chrome on Windows" visitor really looks like Chrome on Windows. A headless browser, an automation flag or a mismatch between the claimed browser and the measured one raises the bot score. See why Cloudflare thinks you are a bot and browser fingerprinting in web scraping.
• Account security. Sites recognize your usual devices and ask for extra verification on a new one.
• Tracking and ads. Third-party scripts can recognize the same browser across sites without cookies. Browsers increasingly block known fingerprinting scripts for this reason.

Common setups are less unique than rare ones: a current Chrome on a popular laptop blends in with many others, while an unusual font set, a rare screen size or an old browser version can make you stand out. Uniqueness also depends on who is measuring: a test site compares you with its own visitors, not with the whole web.

Two ways exist to resist tracking, as the EFF describes them (Cover Your Tracks, Learn):

• Blend in: look exactly like a large group of other browsers, as Tor Browser does.
• Randomize: change some values on every visit so the fingerprint cannot be linked, as Brave does.

The EFF also warns against changing a single value to look more common: the signals are connected, and a mismatch can make you more identifiable, not less.

A fingerprint test shows the values your browser reveals and how rare each one is among the test's own visitors. Read it in this order:

Run the test twice, and once in a private window. Values that change between runs are being randomized by your browser; values that stay the same are the ones that identify you.

You cannot remove a fingerprint, but you can make it less useful for tracking:

• Use a browser with fingerprinting protection. Tor Browser makes users look alike; Brave randomizes some values; Firefox blocks known fingerprinting scripts in its tracking protection and has stricter options (Mozilla Support: Firefox protection against fingerprinting); Safari limits what scripts can read.
• Keep the browser current and common. Default settings, popular fonts and an up-to-date version blend in better than a heavily customized setup.
• Install few extensions. Extensions can change pages in ways scripts detect, which adds identifying detail.
• Separate identities with profiles. A separate browser profile keeps cookies apart, though the device signals stay the same. Tools that give each profile its own fingerprint are covered in fingerprint spoofing and anti-detect browsers.

Blocking JavaScript removes most active signals, but many sites stop working, and the blocking itself is rare enough to stand out.

A proxy changes one signal, the IP address, and leaves the rest of the fingerprint as it was. That still matters in two ways:

• The IP is part of the profile. A new IP from a home internet provider or a mobile carrier separates your sessions at the network level, which a fingerprint alone does not do.
• The IP must agree with the rest. If the proxy IP is in Germany while your browser's time zone and language say California, the mismatch is itself a signal. Pick the proxy location to match the browser profile, or set the profile to match the proxy.

For work that runs several browser profiles, such as managing your own or your clients' social and marketplace accounts, the usual setup is one profile, one fingerprint and one sticky IP per account. ProxyField's sticky sessions keep an IP for 30 s to 36 h, with country, region and city targeting; for weeks on one IP, use a static residential (ISP) proxy. For scraping, see how sites detect proxies, and the residential proxies page for the pool.

Chrome has a fingerprint like any browser, and Chrome on a common Windows or Mac laptop is among the easier setups to blend in with, because so many people use it. Chrome has cut the detail in its User-Agent string and moved much of it into Client Hints, which a site must request (Chromium: User-Agent Reduction). Canvas, WebGL, fonts and screen details stay readable to scripts. Automated Chrome (headless mode, WebDriver) differs from a person's Chrome in ways anti-bot scripts look for, which browser fingerprinting in web scraping covers.

Need IPs that match your browser profiles? ProxyField residential proxies and mobile proxies: country, region and city targeting, sticky sessions up to 36 h, from $1.95/GB with no subscription. Start with the Easy Trial (1 GB); traffic never expires, and all purchases are final.