The MusicBrainz Client Library (libmusicbrainz), also known as mb_client, is a
development library geared towards developers who wish to add MusicBrainz
lookup capabilities to their applications.

Note: Version 5.x and greater support the latest version of the MusicBrainz
web service and are not backwards compatible with earlier versions. As of
2011, version 3.x and below have been deprecated. 

It is safe to have versions 2.x, 3.x, and 5.x on the same system as they don't
conflict with each other.