Is the browser's useragent useless?

Question

because i did'nt (and still do'nt) know what browser's useragent does, i changed it to the beginning of a german classical poem:

Wer reitet so spaet durch Nacht und Wind? Der Vater ist's mit seinem Kind. Er hat den Jungen wohl im Arm, haelt ihn sicher, haelt ihn warm. Mein Vater mein Vater siehst du nicht? Der Erlkoenig zu mir spricht. Sei ruhig, bleib ruhig mein Kind, in duerren Blaettern saeuselt der Wind usw.

With some www-site i verified that it worked. Then i surfed the web and ... and ... nothing happened. I could'nt find any difference between a correct ua and the non-sense above. So my question: Is the ua used at all? Can someone give an example url of a site that changes with different uas? Thanks in advance!

Answer 1

The only time I've used the user-agent string was back i the late 90s when codign javascript - Netscape (now Firefox) and IE had very different supported DOMs, etc so sniffing which was in-use was "helpful".

Typically this was done with "if IE5 is in use, do .... otherwise do ...." - so your total random string wouldn't really break anything. Not so much an issue today since there is better common core functionality as well as various frameworks that do the client-check stuff for you (like angular, vue, etc).

I've also seen some "secure online exam" systems (Respondus Lockdown Browser, etc) and course management systems (WebCT, Angel, Canvas) try to use the user-agent string to confirm that the lock-down browser was in use to prevent copy/pasting, opening other windows, etc. but I've won quite a few bar bets at conferences with vendors of such products by changing the user-agent string in Firefox, etc. and getting right into the "secure no copy/paste" test. For this type of purpose it is absolutely useless.