> could anyone give an example of a modern application that checks against the user agent string?

Gmail. Google docs, every single page titled something demo, ... basically every other site. And it should die already. Browser vendors put up with it because there are thousands and thousands of sites that wouldn't work just because you have the wrong user-agent string and the web developer was incompetent. Great examples include Chrome's idiotic string[1] and Opera's version 9.80[2].

1. Discussed around.

2. http://dev.opera.com/articles/view/opera-ua-string-changes/

I haven't seen web servers send back different pages for non-Mozilla browsers since Mozilla browsers were selectively served frames[0], which is why most User-Agent strings contain "Mozilla". Despite whether this is a good idea or not, it's nostalgically entertaining to see history repeat itself like this.

[0] http://webaim.org/blog/user-agent-string-history/

Chrome?

> Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.31 (KHTML, like Gecko) Chrome/26.0.1410.40 Safari/537.31

For those who wonder how we ended up with such a mess of a user-agent string, this one is a classic: http://webaim.org/blog/user-agent-string-history

I'm thinking he meant more in terms of who builds a website that respects the "like Gecko" in the UA string as UA sniffing has been considered a sub par method for a while now.

I agree with "who does that" because I've never done UA sniffing so I had to look up the term "like Gecko" to even understand the context. As someone else has pointed out, that's for browsers that are not using the Gecko rendering engine. So essentially, everyone is trying to be "like Gecko" in one way or another.

I meant 'who does check that user agent', edited to clarify.

A lot of people, on Firefox OS we have a blacklist of sites we have to send Android like user agents to so we are served mobile friendly content: https://github.com/mozilla-b2g/gaia/blob/master/build/ua-ove...

Its a sad situation.

See also: https://github.com/operasoftware/browserjs/blob/master/deskt...

YouTube is a particularly bad offender. Linked to their mobile site on a desktop? You get the ultra-basic WAP-like version, instead of the smartphone version or a redirect to the desktop version. Linked to their mobile site in Opera Mini? Yep, WAP-like version, despite the fact that Opera Mini would have no problems with the smartphone version.

Last I checked, Google+ had an User-Agent whitelist. Anything not in the list would get a "Your browser is too old, please upgrade" page.

> example of a modern application that checks against the user agent string?

I don't think this is aimed at fixing modern applications. It is aimed at much older ie 6-8 era code still on the web that has a bunch of hacks.