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What is a browser fingerprint?

Browser and device characteristics can remain as correlation material even after cookies are deleted.

If you delete cookies, websites will no longer know that you are the same user.

That way of thinking is not enough. Websites do not distinguish users only with cookies. Browser type, OS, screen size, language, time zone, supported fonts, Canvas and WebGL rendering results, extensions, and other details also become characteristics of the environment.

The idea of combining these characteristics to infer that the same browser environment is being used is a browser fingerprint.

This article explains the basics of browser fingerprints and their impact on anonymity. More detailed content is covered in "Browser fingerprinting basics."

Fingerprint basics

A browser fingerprint is a way of combining browser and device characteristics as identifying material.

Unlike a method that resends a stored identifier, such as a cookie, the material is information the browser exposes in order to display a page.

Information	What it shows	Anonymity caution
User-Agent	Browser and OS type	Becomes a broad characteristic of the usage environment
Screen size	Device or display environment	Can signal that it is the same environment
Language settings	Preferred language	A clue to region or user attributes
Time zone	Device time setting	Can connect to where and when you are active
Fonts	OS or installation environment	Unusual combinations stand out
Canvas/WebGL	Rendering results	Differences in GPU or browser can appear

Each item is weak information on its own.

But when combined, they become a characteristic. For anonymity, this "combination" is the problem.

Differences from cookies

Cookies are data stored in the browser.

Websites use cookies to handle login state and return visits. If you delete cookies, that stored information can be removed.

By contrast, a fingerprint uses how the browser environment appears as its material.

Item	Cookie	Fingerprint
Material	Stored identifier	Browser and device characteristics
User awareness	Easy to delete	Hard to tell what is being used as material
How to change it	Delete cookies	Change environment or settings
Impact on anonymity	Re-identification within the same site	Signals that it is the same environment can remain even without cookies
Caution	Connects to login state	Custom settings can stand out

Cookie defenses and fingerprint defenses are different.

Even if you delete cookies, if the browser characteristics are the same, material for correlation remains.

Why Custom Settings Stand Out

When trying to increase anonymity, it can be tempting to customize the browser in detail.

Ad blocking, special font settings, uncommon extensions, fine-grained JavaScript controls. These can be useful in some situations. However, when the combination becomes unusual, it becomes a characteristic of that environment alone.

Setting	Useful aspect	Why it stands out
Many extensions	Reduces tracking and ads	The combination becomes unusual
Special screen size	Makes work easier	Becomes a characteristic different from other users
Added fonts	Improves display	The installation environment becomes visible
Fine-grained blocking settings	Reduces unnecessary communication	Site-by-site behavior becomes a characteristic
Custom User-Agent	Intended to hide information	Can instead look unnatural

For anonymity, adding settings that look strong is not always the right answer.

In some situations, it is more important to align the visible environment with many other users.

Relationship With Tor Browser

Tor Browser is designed not only to use the Tor network, but also to align how the browser appears.

This is to reduce differences between users and make identification by fingerprinting harder.

If you use Tor Browser, adding extensions or making major changes to screen size or settings can move you away from the standard state and make you stand out.

Action	Effect	Caution
Use the standard settings	Looks closer to other users	Do not break the basics
Install extensions	Creates custom characteristics	Weakens anonymity
Change screen size in a custom way	Screen characteristics may appear	Understand Tor Browser behavior
Log in with a real-name account	Links through the account	A problem before the network route
Mix with a regular browser	Cookies and history get mixed	Environment separation is necessary

Tor Browser is powerful, but its protection can be undermined by how it is used.

What to do

Fingerprint defenses are not about adding more detailed settings.

First, separate real-name use from anonymous use. The basics are not reusing the same browser, the same extensions, the same cookies, or the same login state.

Check item	Reason
Did you separate real-name use and anonymous use?	Do not mix browser characteristics and cookies
Have you added too many extensions?	Avoid becoming an unusual environment
Do screen size or language settings stand out?	Do not make environment characteristics stronger
Have you kept Tor Browser's standard settings?	Align the visible environment with other users
Is login state still present?	Avoid correlation through accounts

Rather than trying to erase fingerprints completely, it is more realistic to reduce correlation together with cookies, logins, IP addresses, and post content.

Scope Covered Here

This article covers an overview of browser fingerprints.

It does not cover tracking technologies for individual sites, detailed measurement methods for Canvas or WebGL, or the behavior of each extension.

The important point is to understand that information automatically exposed by the browser also relates to anonymity. Not only the information you type, but the environment itself can become a clue.

Failure Examples

Fingerprint failures do not happen only through special attacks.

Using your everyday browser as-is. Installing the same extensions used for real-name activity into an anonymous browser. Having the same screen size, language settings, fonts, and login state as real-name use. These accumulated details create signs of the same environment.

Failure	What happens	Countermeasure
Use the real-name browser	History and saved state get mixed	Use a dedicated environment
Match extensions	Signals that it is the same environment appear	Keep the anonymous environment minimal
Add custom settings	The environment becomes unusual	Do not move too far from standard settings
Log in with a real-name account	Links through the account	Do not log in
Operate long-term on the same device	Characteristics accumulate	Review the environment periodically

Summary

A browser fingerprint is the idea of combining browser and device characteristics to infer that the same environment is being used.

Even if you delete cookies, characteristics such as screen size, language, time zone, fonts, Canvas, WebGL, and extensions remain.

For anonymity, adding custom settings is not always safe.

Instead, becoming an unusual environment can make you stand out.

A fingerprint alone does not determine all of anonymity. However, when combined with IP address, cookies, login state, post content, and time, it becomes a strong clue.

Related tools

Public IP Check

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