Rob Allen quickly points out a tool that Lucene users (Zend Framework and otherwise) can use to check out the contents of their indexing files.

If you want to understand what's in your Zend_Search_Lucene index files, then download Luke (http://www.getopt.org/luke/) and point it at the directory containing your index files.

He also includes a screenshot to give you an idea of the interface.

Luke bills itself as: "a handy development and diagnostic tool, which accesses already existing Lucene indexes and allows you to display and modify their contents in several ways [including] view documents / copy to clipboard, selectively delete documents from the index and optimize indexes".