User-Agent Parser

User-Agent（UA） It is a string attached by the browser or client application when sending an HTTP request, used to identify its own name, version, operating system, rendering engine and other information. Pioneered by Netscape in the 1990s, the format has evolved over the years and is now part of the Internet infrastructure.

Typical UA string format is as follows:
Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/140.0.0.0 Safari/537.36

The server provides corresponding content, adjusts layout or counts traffic sources by parsing UA.

This is a classic problem left over from Internet history. The original Netscape browser's UA began with "Mozilla" (Mozilla was Netscape's internal code name). Later, in order to ensure that Microsoft's IE could obtain web pages that supported full functionality, it disguised its UA as Mozilla compatible and added the "Mozilla/4.0" prefix.

Later, browsers based on the Gecko engine (such as Firefox) used the "Mozilla/5.0" prefix, while browsers based on the WebKit/Blink engine (Chrome, Safari, Edge) also continued to use the "Mozilla/5.0" prefix for compatibility. So the UA of all modern browsers starts with "Mozilla/5.0", forming a de facto standard.

User-Agent is useful butNot 100% reliable, the main reasons include:

1. Easy to counterfeit (Spoofing): Browsers and crawlers can easily modify the UA string and pretend to be other clients.
2. Historical compatibility baggage: As mentioned before, all browsers claim "Mozilla/5.0", making parsing complicated.
3. Privacy mode and blocking: Some browsers allow users to customize or hide UA.
4. Client Hints: Modern browsers are gradually replacing UA with Client Hints API to provide more accurate and controllable device information.

Therefore, UA resolution is suitable for statistical analysis and general identification, but UA alone should not be relied upon in security decisions (such as fraud prevention).

Client Hints It is a new standard developed by W3C and aims to replace the traditional User-Agent string. Unlike UA, Client Hints allow browsersselectively Provide device and browser information to the server instead of exposing the entire UA string at once.

Key differences:
• selective disclosure: The server can pass HTTP headers such as Accept-CH) requests specific information, and the browser then decides whether to respond.
• structured data: Information is passed in the form of key-value pairs (such as Sec-CH-UA: "Chrome";v="140"), the analysis is more precise.
• Reduce UA bloat: As Client Hints become more popular, the content of the UA string will be gradually simplified.

Currently, mainstream browsers such as Chrome and Edge already support Client Hints, but it will still take several years to fully replace UA.

Browser Engine Also known as the Rendering Engine, it is the core component of the browser and is responsible for parsing and rendering HTML, CSS and JavaScript into web pages seen by users.

Currently the main browser engines:
• Blink: Developed by Google and used in Chrome, Edge, Opera, Brave, etc., it is currently the engine with the highest market share.
• WebKit: Developed by Apple and used in Safari and all browsers on iOS (Apple requires WebKit for iOS browsers).
• Gecko: Developed by Mozilla and used in Firefox.
• Trident: Microsoft legacy engine for Internet Explorer (no longer supported).
• EdgeHTML: The engine used by Microsoft's legacy Edge (deprecated in 2020 in favor of Blink).

Different rendering engines may have different levels of support for web standards, which is why web development requires cross-browser testing.

Search engine bots (such as Googlebot, Bingbot) usually useExplicit UA string, easy for website administrators to identify. However, some crawlers pretend to be human browser UA to bypass blocks or retrieve content, which is known as UA Spoofing。

The Bot detection function of this tool is based on the UA characteristics of known Bots, but please note:Not guaranteed to be 100% accurate. Advanced crawlers can forge UA strings that are exactly the same as real browsers. For more accurate Bot protection, it is recommended to combine multi-layer mechanisms such as IP reputation scores, behavioral analysis, and verification codes (CAPTCHA).

Not at all. This tool isPure front-end application, all User-Agent parsing, Bot detection and Raw Analysis are done locally in your browser, no data is sent to the server. Works even when offline.

The "Get current UA" function is to read directly navigator.userAgent, this information is made public by your browser and remains only on your device.