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
facter will load the puppet libraries and also show the puppet specific
facts, including any custom ones you have deployed via puppet.