Package cdxj implements the CDXJ file format used by OpenWayback 3.0.0 (and later) to index web archive contents (notably in WARC and ARC files) and make them searchable via a resource resolution service. The format builds on the CDX file format originally developed by the Internet Archive for the indexing behind the WaybackMachine. This specification builds on it by simplifying the primary fields while adding a flexible JSON 'block' to each record, allowing high flexiblity in the inclusion of additional data.