The Widget Laboratory is a desktop application for previewing gtk and metacity themes. It updates the preview whenever the theme files change, so it can be used to make editing gtk themes faster and easier.
Install it from the PPA: https:/
All bugs Latest bugs reported
Bug #544756: TWL doesn't appear if GTK theme has no Metacity
Reported on 2010-03-23
Bug #480064: twl doesn't start (D-Bus-Type Error)
Reported on 2009-11-10