User Agent List

20 June 2005

Whenever a web browser gets a webpage is passes some information known as the User Agent information. This allows some websites to tailor different versions of their site for different browsers (although far better to just make the page work in different browsers), and is probably most used by webmasters wanting to check what browsers are being used by visitors.

The problem is that there is no standard for how the user agent information should be formatted. As a result it's a difficult task to program how this is handled. It's made even more difficult by some browsers pretending they are a different browser. Internet Explorer was the first to do this by pretending to be Netscape so that pages designed for Netscape worked with IE.

I've now found a useful site at www.phsychedelix.com/agents.html. Excusing the colour scheme (the website name gives you a bit of a clue there), the site provides the most comprehensive list of user agent strings with details of which browsers use the string. Using this I've been able to improve the browser detection on my Apache LogInfo Program. It's not available yet, but will be included in the next version which I'll announce here once available.

Here are some of the key figures for this website:
Browsers:

MSIE 6	46 %
Firefox 1	29 %
unknown	10 %
MSIE 5	4 %

Operating System

Windows XP	39 %
Linux	20 %
Windows 2000	15 %
unknown	10 %

There are still a number of unknowns, but these are where the browser doesn't give the details. These are perhaps web robots or similar.