puppetlabs/puppetdb — pull request #312 by nicklewis (2012-10-05 18:51:26+00:00)
Title: Add a /v2/fact-names route which returns the list of known facts

The results are return as an alphabetically-sorted JSON array of
distinct fact names. This is helpful for applications where it's useful
to know up-front which facts are available, rather than having to query
for the entire set of all facts in order to get that information.