You're right: Xcode includes its own set of CLTs namespaced under /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.

You're right: Xcode includes its own set of CLTs namespaced under /Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX10.9.sdk/, but that's useless for anything expecting FHS. What xcode-select --install will do is the same thing as downloading and installing the standalone CLT package manually, but in a manner similar to how X11 used to be distributed: OS X will request permission to download the standalone CLT package and install it: http://i.imgur.com/O1CIGCP.png http://i.imgur.com/O1CIGCP.png It also doesn't currently work (it'll error out saying it's not available on the Software Update Server). Assuming that's fixed by release, it will save a trip to the web browser to download it manually.