What Is Browser Fingerprinting? How It Works, What It Collects and How to Test Yours (2026)

What is browser fingerprinting? #

Think of recognising someone by their handwriting instead of their name tag. A website can't read your name from your browser, but it can see a collection of settings and characteristics, and that collection is often distinctive enough to recognise the same browser again.

The W3C defines browser fingerprinting as the capability of a site to identify or re-identify a visiting user, user agent or device through configuration settings or other observable characteristics.

What does a fingerprint contain? #

EFF's Cover Your Tracks lists the kind of information it measures:

No single item identifies you. It is the combination that can be distinctive.

Why cookies and IP addresses don't change it #

Cookies and IP addresses are different identifiers. A fingerprint comes from your browser's configuration and settings, so, as EFF puts it, clearing your cookies doesn't help. A VPN or proxy changes the IP address a site sees, and incognito mode stops local history, but neither changes the configuration the fingerprint is built from. See Antidetect browser vs VPN vs incognito.

Is every browser unique? #

Not necessarily. How identifiable a browser is depends on how common its combination of settings is. A very common setup blends into a large group, while an unusual combination of fonts, extensions and settings can stand out. EFF's tool reports how your browser compares with others it has measured.

Test yours in two minutes #

1. Open EFF's Cover Your Tracks and start the test.
2. Read the result: how identifiable your browser looks, and which characteristics contribute most.
3. Change one thing, for example install or remove an extension, then run it again.
4. Run it in a different browser, or inside a separate browser profile, and compare.

The value of the test is comparison: it shows how your setup differs from others, not a pass or fail.

What reduces it #

• Keep your setup ordinary. Unusual settings and many extensions can make a browser stand out.
• Keep your software updated.
• Use a browser or tool with fingerprinting protection, and read what it actually does.
• Separate your purposes. Use separate browser environments for separate roles, so one setup doesn't tie everything together.

The W3C is realistic about the limits: complete elimination of fingerprinting by a determined adversary, through widely deployed technical means alone, is implausible. The aim is to reveal less, not nothing.

Who uses fingerprinting, and why? #

Fraud prevention and security teams use it to notice unusual sessions. Analytics and advertising systems use it to recognise returning visitors. The same capability raises privacy concerns, which is why the W3C publishes guidance for people who design web features. A survey of the research (Laperdrix et al., 2019) describes how fingerprints work and categorises the defences.

Fingerprints and managing several accounts #

When you manage several accounts you own or are authorised to run, such as client or brand accounts, running them all from one browser setup makes them look alike to a site. That is why people keep each account in its own browser environment: its own cookies, its own device and browser settings, and its own proxy. See what a browser profile is.

Each ADSSPEED profile has its own device and browser configuration, plus its own proxy. Use it only for accounts you own or are authorised to manage, and follow each platform's rules.