YARI is a comprehensive tool suite to debug, spy, spider, inspect and navigate Eclipse based application GUIs (Workbench or RCP).
If you want to know how your swt ui is built up or which plugins contribute to your eclipse workbench YARI will offer you all the information needed. It allows you to have a deep look into the swt or eclipse internals. Search an id for a menu contribution, find a contributing plugin or debug the swt/jface ui (e.g. figure out layout problems) is a core feature of the tool.