Browser fingerprinting: how sites recognise you without cookies

A browser fingerprint is the combination of small technical details your browser gives to every site. Together they can single out one device among millions.

The idea

No single detail on our home page identifies you. Millions of people use the same browser version, and millions have the same screen size. But put twenty such details side by side (browser, system, screen, time zone, languages, fonts, graphics chip and more) and the combination becomes rare, sometimes unique. A site that records the combination can recognise the same browser again, with no cookie and even in a private window.

What goes into a fingerprint

• User agent: browser and system names and versions. See your user agent.
• Screen: size, pixel ratio, colour depth. See your screen.
• Time zone and languages.
• Fonts installed on the device.
• Canvas and WebGL: the page asks the browser to draw hidden text or shapes. Tiny differences between graphics chips and drivers make the result differ from device to device.
• Audio processing, measured the same way.
• Hardware hints: number of processor threads, memory, touch support.
• Settings: cookies allowed or not, "do not track", content blockers detected.
• Your IP address, which sits beside the fingerprint and helps link visits.

Who uses it and why

• Banks and payment services use it to notice when a login comes from a device they have never seen. This protects accounts.
• Fraud and bot detection on shopping and ticket sites.
• Advertising and tracking companies use it to follow people who block cookies. This is the use that privacy rules and browser makers push against.

What reduces it, honestly

There is no switch that makes you invisible, and some popular advice makes things worse.

1. Use a browser with built-in protection. Firefox (Enhanced Tracking Protection), Safari and Brave block known fingerprinting scripts or blur the values they read. The Tor Browser goes furthest by making every user look the same.
2. Keep the browser ordinary. Each unusual extension, font or setting makes you stand out more. A long list of privacy extensions is itself a fingerprint.
3. Keep the browser updated, so you sit in the largest crowd.
4. Separate your activities. A different browser, or a different browser profile, for logged-in work and for casual browsing stops the two being linked easily.
5. Do not rely on these alone: private windows clear cookies but leave the fingerprint unchanged; a VPN changes the address but nothing else.

What we do on this site

The details on our home page are read by your own browser and shown to you. They are not sent to us or stored. The page is a mirror, so that you can see what any site you visit is able to read.