So, been a while since I've played, I don't think I have tried to get into the game since I upgraded to El Capitan on my Mac OS X El Capitan 10.11.2. It gives me the prompt "To use the "java" command-line tool you need to install a JDK" and some link to the Java Developer Kit site. Is this a Steam related problem? The only stuff I could find in the forums was rather old.
EDIT: Might be working, waiting on a loonnggg patch lol. Downloaded the link here and it didn't give the prompt for Java anymore: https://support.apple.com/kb/dl1572?locale=en_US
Yeah, I'm getting the exact same issue. Did the patch work for you? I'm in bad need of a way to play spiral knights on my laptop, and this is the only post relevant to the issue.