You want to see all the facts available to you.
# show all facter facts facter # show all facter facts, and those defined for use in puppet (run as root) facter -p
While facter is heavily used by puppet the facter tool itself can be run as a standalone program or included as a library in your own ruby code.
Running facter with no arguments will list all the facts and their values that facter knows about. When invoked with the “-p” option facter will load the puppet libraries and also show the puppet specific facts, including any custom ones you have deployed via puppet.