xctool does not yet support Xcode 7 in the latest stable release.
As a workaround, you can install the development version by adding the following to your circle.yml file.
brew uninstall xctool && brew install --HEAD xctool
*Credits: Originally posted by @alexey
Looks like 0.2.6+ supports Xcode 7, which is what brew installs for me now.
@alexey Can we bake in this version in the future VM release?
@cvermilion thanks so much for letting us know! 
You’re welcome! Mostly I’m just trying out the discussion board, haven’t used Discourse before. 
@levlaz Of course, will do.
We are really happy with Discourse so far, let me know what you think after you have had time to play with it a bit!
Will do! (Hmm, that seems to be a useful reply under 20 characters that isn’t quite communicated by the like button…)
I think the 20 character limit is mostly for spam :), maybe we can lower it to 10 or something until things get out of control.
@alexey released a new OS X image which should have the proper working version of xctool now