The IE10 User-Agent String

April 15th, 2011

We recently announced IE10 Platform Preview 1. Aside from some exciting new features, this platform preview also includes the new IE10 user-agent string:

 Mozilla/5.0 (compatible; MSIE 10.0; Windows NT 6.1; Trident/6.0)

Overall this represents a natural evolution of the IE9 user-agent string with only two changes:

  • The value of the “MSIE” token is now “10.0”
  • The value of the “Trident” token is now “6.0”

Also, Compatibility View still maps to IE7 Standards Mode just like in IE8 and IE9. Here the user-agent string mimics IE7 for compatibility, but the “Trident” token is now “6.0” to signify IE10 is in use.

 Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; Trident/6.0)

Does this affect me?

Ideally, very few people should care about these changes. In particular, those of you using feature detection exclusively can sit back and relax.

However if your site is still using user-agent sniffing, then increasing the “MSIE” token to “10.0” is particularly noteworthy. Why? Because it adds an extra digit to the string value of the token. Most sites will handle this effortlessly, but some will process the extra digit incorrectly, causing them to identify IE10 as IE1.

To help illustrate, here’s a regular expression that only captures the first digit of the “MSIE” token’s value:

 // INCORRECT: will report IE10 version in capture 1 as "1" var matchIE = /MSIE\s(\d)/;

And here’s one that captures the full value of the “MSIE” token:

 // Correct: will report IE10 version in capture 1 as "10.0" var matchIE = /MSIE\s([\d.]+)/

Of course your code may look significantly different depending on your choice of programming language, approach to string parsing, etc. Those of you with custom HTTPS configurations on Apache may also want to read this blog post by Eric Lawrence.

Call to action

Download IE10 Platform Preview 1 to test how your site responds to IE10’s user-agent string. Update your user-agent sniffing logic if necessary, or even better, consider migrating to feature detection to make worrying about changes like this a thing of the past.

—Tony Ross, Program Manager, Internet Explorer