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User agent를 이용한 브라우저 감지

현재 번역은 완벽하지 않습니다. 한국어로 문서 번역에 동참해주세요.

보통 브라우저마다 다른 웹 페이지 또는 서비스를 제공하는 것은 나쁜 생각입니다. 웹은 사용자가 어떤 브라우저나 디바이스를 사용하고 있는지 개의치 않고 모두에게 접근성이 용이해야 하기 때문입니다. 따라서 특정 브라우저를 타겟으로 개발하는 것보다 가용적인 기능들 (예를 들어 Web API 등)을 이용하여 당신의 웹 사이트를 개선하는 것을 추천합니다.

하지만 브라우저와 웹 표준은 완벽하지 않고 그 간격은 여전히 브라우저 감지 기능을 필요로 합니다. User-Agent를 사용하여 브라우저를 감지하는 것은 간단해 보이지만, 사실 그것을 잘 이용하는 것은 무척 힘든 일입니다. 이 문서는 user agent를 이용하여 브라우저를 감지하는 일을 올바르게 가이드합니다.

주의하세요! user agent 정보를 가로채는 것은 좋은 아이디어가 아닙니다. 대부분의 경우 호환성이 뛰어난 좋은 다른 해결방안을 찾을 수 있을 것입니다.

브라우저 감지 기능을 사용하기 전 고려할 사항들

첫 번째로 user agent 문자열 정보를 이용하여 브라우저를 감지하기 전에 최대한 사용안하는 것을 고려하십시오. 내가 이 기능을 원했는지 다시 한 번 스스로 확인하시길 바랍니다.

혹시 브라우저의 특정 버전에서의 버그를 고치려고 합니까?
포럼에서 찾아보십시오. 만약 이 버그를 당신이 처음 발견했다면 포럼에 질문을 하십시오. 또한 전문가나 다른 견해를 가진 이들이 이 버그를 해결하는데 도움을 줄 것입니다. 만약 버그가 좀처럼 없는 문제라면 브라우저 벤더의 버그 추적 시스템 (Mozilla; WebKit; Opera)에서 보고된 버그인지 확인하십시오. 
Are you trying to check for the existence of a specific feature?
Your site needs to use a specific Web feature that some browsers don't yet support, and you want to send those users to an older Web site with fewer features but that you know will work. This is the worst reason to use user agent detection, because odds are eventually all the other browsers will catch up. You should do your best to avoid using user agent sniffing in this scenario, and do feature detection instead.
Do you want to provide different HTML depending on which browser is being used?
This is usually a bad practice, but there are some cases in which this is necessary. In these cases, you should first analyze your situation to be sure it's really necessary. Can you prevent it by adding some non-semantic <div> or <span> elements? The difficulty of successfully using user agent detection is worth a few disruptions to the purity of your HTML. Also, rethink your design: can you use progressive enhancement or fluid layouts to help remove the need to do this?

Avoiding user agent detection

If you want to try to avoid using user agent detection, there are options in some cases!

Feature detection
Feature detection is where you don't try to figure out which browser is rendering your page, but instead you check to see if the specific feature you need is available. If it's not, you use a fallback. However, never use feature detection in the rare cases when you actually want browser detection, since other browsers may implement the feature in the future, but differently. Bugs caused by this can be insidiously hard to find and fix.
Progressive enhancement
This design technique involves developing your Web site in 'layers', using a bottom-up approach, starting with a simpler layer and improving the capabilities of the site in successive layers, each using more features.
Graceful degradation
This is a top-down approach in which you build the best possible site using all the features you want, then tweak it to make it work on older browsers. This can be harder to do, and less effective, than progressive enhancement, but may be useful in some cases.

Which part of the user agent contains the information you are looking for

As there is no uniformity of the different part of the user agent string, this is the tricky part.

Browser Name

When people say they want "browser detection", often they actually want "rendering engine detection". Do you actually want to detect Firefox, as opposed to SeaMonkey, or Chrome as opposed to Chromium? Or do you actually simply want to see if the browser is using the Gecko or the WebKit rendering engine? If this is what you need, see further down the page.

Most browser set the name and version in the format BrowserName/VersionNumber, with the notable exception of Internet Explorer. But as the name is not the only information in a user agent string that is in that format, you can not discover the name of the browser, you can only check if the name you are looking for. But note that some browsers are lying: Chrome for example reports both as Chrome and Safari. So to detect Safari you have to check for the Safari string and the absence of the Chrome string, Chromium often reports itself as Chrome too or Seamonkey sometimes reports itself as Firefox.

Also pay attention not to use a simple regular expression on the BrowserName, user agents also contain strings outside the Keyword/Value syntax. Safari & Chrome contain the string 'like Gecko', for instance.

  Must contain Must not contain  
Firefox Firefox/xyz Seamonkey/xyz  
Seamonkey Seamonkey/xyz    
Chrome Chrome/xyz Chromium/xyz  
Chromium Chromium/xyz    
Safari Safari/xyz Chrome/xyz or Chromium/xyz Safari gives two version number, one technical in the Safari/xyz token, one user-friendly in a Version/xyz token

OPR/xyz [1]

Opera/xyz [2]


[1]  Opera 15+ (Blink-based engine) 

[2] Opera 12- (Presto-based engine)

Internet Explorer ; MSIE xyz;   Internet Explorer doesn't put its name in the BrowserName/VersionNumber format

Of course, there is absolutely no guarantee that another browser will not hijack some of these things (like Chrome hijacked the Safari string in the past). That's why browser detection using the user agent string is unreliable and should be done only with the check of version number (hijacking of past versions is less likely).

Browser version

The browser version is often, but not always, put in the value part of the BrowserName/VersionNumber token in the User Agent String. This is of course not the case for Internet Explorer (which puts the version number right after the MSIE token), and for Opera after version 10, which has added a Version/VersionNumber token.

Here again, be sure to take the right token for the browser you are looking for, as there is no guarantee that others will contain a valid number.

Rendering engine

As seen earlier, in most cases, looking for the rendering engine is a better way to go. This will help to not exclude lesser known browsers. Browsers sharing a common rendering engine will display a page in the same way: it is often a fair assumption that what will work in one will work in the other.

There are five major rendering engines: Trident, Gecko, Presto, Blink and WebKit. As sniffing the rendering engines names is common, a lot of user agents added other rendering names to trigger detection. It is therefore important to pay attention not to trigger false-positives when detecting the rendering engine.

  Must contain  
Gecko Gecko/xyz  
WebKit AppleWebKit/xyz Pay attention, WebKit browsers add a 'like Gecko' string that may trigger false positive for Gecko if the detection is not careful.
Presto Opera/xyz Note: Presto is no longer used in Opera browser builds >= version 15 (see 'Blink')
Trident Trident/xyz Internet Explorer put this token in the comment part of the User Agent String
Blink Chrome/xyz  

Rendering engine version

Most rendering engine put the version number in the RenderingEngine/VersionNumber token, with the notable exception of Gecko. Gecko puts the Gecko version number in the comment part of the User Agent after the rv: string. From Gecko 14 for the mobile version and Gecko 17 for the desktop version, it also puts this value in the Gecko/version token (previous version put there the build date, then a fixed date called the GeckoTrail).


The Operating System is given in most User Agent strings (although not web-focussed platforms like Firefox OS), but the format varies a lot. It is a fixed string between two semi-colons, in the comment part of the User Agent. These strings are specific for each browsers. They indicates the OS, but also often its version and information on the relying hardware (32 or 64 bits, or Intel/PPC for Mac).

Like in all cases, these strings may change in the future, one should use them only in conjunction for the detection of already released browsers. A technological survey must be in place to adapt the script when new browser versions are coming out.

Mobile, Tablet or Desktop

The most common reason to perform user agent sniffing is to determine which type of device the browser runs on. The goal is to serve different HTML to different device types.

  • Never assume that a browser or a rendering engine only runs on one type of device. Especially don't make different defaults for different browsers or rendering engines.
  • Never use the OS token to define if a browser is on mobile, tablet or desktop. The OS may run on more than one type of (for example, Android runs on tablets as well as phones).

The following table summarizes the way major browser vendors indicate that their browsers are running on a mobile device:

Common browsers User Agent strings
Browser Rule Example
Mozilla (Gecko, Firefox) Mobile or Tablet token in the comment. Mozilla/5.0 (Android; Mobile; rv:13.0) Gecko/13.0 Firefox/13.0
WebKit-based (Android, Safari) Mobile Safari token outside the comment. Mozilla/5.0 (Linux; U; Android 4.0.3; de-ch; HTC Sensation Build/IML74K) AppleWebKit/534.30 (KHTML, like Gecko) Version/4.0 Mobile Safari/534.30
Blink-based (Chromium, Google Chrome, Opera 15+) Mobile Safari token outside the comment Mozilla/5.0 (Linux; Android 4.4.2); Nexus 5 Build/KOT49H) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/33.0.1750.117 Mobile Safari/537.36 OPR/20.0.1396.72047
Presto-based (Opera 12-)

Opera Mobi/xyz token in the comment (Opera 12-)

Opera/9.80 (Android 2.3.3; Linux; Opera Mobi/ADR-1111101157; U; es-ES) Presto/2.9.201 Version/11.50

Internet Explorer IEMobile/xyz token in the comment. Mozilla/5.0 (compatible; MSIE 9.0; Windows Phone OS 7.5; Trident/5.0; IEMobile/9.0)

In summary, we recommend looking for the string “Mobi” anywhere in the User Agent to detect a mobile device.

If the device is large enough that it's not marked with “Mobi”, you should serve your desktop site (which, as a best practice, should support touch input anyway, as more desktop machines are appearing with touchscreens).

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