  We present the Open Supernova Catalog, an online collection of observations
and metadata for presently 36,000+ supernovae and related candidates. The
catalog is freely available on the web (https://sne.space), with its main
interface having been designed to be a user-friendly, rapidly-searchable table
accessible on desktop and mobile devices. In addition to the primary catalog
table containing supernova metadata, an individual page is generated for each
supernova which displays its available metadata, light curves, and spectra
spanning X-ray to radio frequencies. The data presented in the catalog is
automatically rebuilt on a daily basis and is constructed by parsing several
dozen sources, including the data presented in the supernova literature and
from secondary sources such as other web-based catalogs. Individual supernova
data is stored in the hierarchical, human- and machine-readable JSON format,
with the entirety of each supernova's data being contained within a single JSON
file bearing its name. The setup we present here, which is based upon open
source software maintained via git repositories hosted on github, enables
anyone to download the entirety of the supernova dataset to their home computer
in minutes, and to make contributions of their own data back to the catalog via
git. As the supernova dataset continues to grow, especially in the upcoming era
of all-sky synoptic telescopes which will increase the total number of events
by orders of magnitude, we hope that the catalog we have designed will be a
valuable tool for the community to analyze both historical and contemporary
supernovae.
