Browser fingerprinting: what it is and how it works

Every time you open a website, your browser tells it dozens of small facts about itself. None of them identifies you on its own. Together they often do. That combination is called a browser fingerprint.

Check your browser right now

Checking your browser…

What goes into a fingerprint

A fingerprint is built from properties that any page can read without asking for permission:

The User-Agent and Client Hints: browser, version, operating system, and on mobile often the device model.
Screen size, available area, color depth and pixel ratio.
Time zone, languages and locale formatting.
Hardware hints: number of CPU cores, approximate memory, touch support.
The graphics card name exposed by WebGL, and the way your GPU renders a test image (canvas and WebGL fingerprints).
How your audio stack processes a test signal (audio fingerprint).
Installed fonts, speech synthesis voices, the number of microphones, speakers and cameras.

Each property alone is shared by millions of people. But a specific mix of GPU, fonts, screen and time zone can be rare enough to recognise the same browser across sites and visits, without any cookies.

Why rendering fingerprints work

Canvas, WebGL and audio fingerprints rely on tiny differences in how hardware, drivers and software draw shapes and process sound. Two computers with different graphics cards or driver versions produce slightly different pixels for the same drawing instruction. A script draws a hidden image, turns the pixels into a short hash and gets a value that stays the same on one device and differs between many others.

What fingerprinting is used for

There are two very different uses. Advertisers and trackers use fingerprints to follow people across sites when cookies are blocked, which is why privacy browsers fight them. Security systems use them to protect accounts and payments: a login from a browser that has never been seen before, or one that looks forged, gets an extra check. Banks, marketplaces and ticket sellers rely on this to stop bots, account takeovers and multi-accounting.

Uniqueness and consistency

For tracking, what matters is how unique a fingerprint is. For security, a second question matters just as much: is the fingerprint consistent? A real browser reports facts that fit together. A browser that lies, because an antidetect tool or an extension changed some values, often leaves contradictions: a Windows User-Agent with a graphics card that exists only in Macs, a time zone that does not fit the IP country, or a background Web Worker that reports a different browser than the page. Anti-fraud systems look for exactly these seams.

How privacy browsers deal with it

There are two strategies. Tor Browser and Firefox with resistFingerprinting make users look alike: standard window sizes, the UTC time zone, a fixed set of values. Brave gives each site slightly different, randomized values for canvas, audio and some other features, so fingerprints cannot be linked across sites. Both are legitimate privacy protection, and a good checker should recognise them instead of calling them fake.

How to see your own fingerprint

The SpoofLens check on this page collects these signals in your browser, adds what our server sees (the network of your IP and the headers your browser sent) and compares everything. You get a fingerprint ID, a truth index from 0 to 100 and a list of contradictions, if there are any. Nothing is stored.

Frequently asked questions

Can I avoid being fingerprinted?: Not completely, since any page can read basic properties. You can reduce tracking with a browser that has built-in protection (Tor Browser, Firefox with strict settings, Brave) and by blocking third-party trackers. Making your browser very unusual can make it easier to recognise, not harder.
Is fingerprinting legal?: It depends on the purpose and the country. In the EU, regulators treat fingerprinting for tracking much like cookies, so it generally needs consent, while keeping a service secure can fall under exemptions. This is general information, not legal advice.
Does a VPN change my fingerprint?: No. A VPN changes your IP address, not your browser properties. It can even add a contradiction if your time zone and language stay those of your real country.