What is a User-Agent and what information does it carry?

What information does a User-Agent string contain?

A User-Agent string packs the browser name and version, operating system type and version, and sometimes the device type, all into a single line. Browsing with Chrome on Windows, for example, sends a string containing information related to both "Windows" and "Chrome."

ipnow.kr shows the raw string as-is, and also breaks it down into parsed fields such as browser, browser_version, os and device.

What is a User-Agent actually used for?

Websites use it to decide whether to show a desktop or mobile layout, and to gather statistics on visitors' browsers and devices. It is also used to warn users of older browsers that a feature is not supported.

Some sites also use it to filter automated traffic, restricting access when a User-Agent looks abnormal or matches a known bot pattern.

Can a User-Agent alone identify me?

A User-Agent alone is unlikely to pinpoint an individual, but combined with other signals such as IP address or screen size, it can help narrow down which specific browser environment a visitor is using.

What are User-Agent Reduction and Client Hints?

Major browsers have been reducing the detailed version information packed into the User-Agent string, a trend known as User-Agent Reduction. It is a privacy measure meant to prevent a single string from identifying a visitor too precisely.

In its place, a mechanism called Client Hints lets a website request only the specific information it actually needs, such as an exact OS version, on a case-by-case basis. The overall direction is moving away from one long string toward exchanging only what is needed.