Luke, the tool to inspect Lucene indexes, is great and comes in handy if you work with Lucene. Unfortunately development seems to have slowed down (which is totally understandable to me, LIRE does the same all the time:)
However, the current binary is not able to open indexes for Lucene 4.2, neither is the SVN version. Still, Luboš Košco made an effort and put the source of an adapted version online. (Thanks to Luboš at this point!)
I basically just did the trick of cloning the repository and running the ant task to create the binary, but I still need to publish it for those who don’t want to compile their own version. Feel free to download it and use: Download luke-4.2.0.jar
Basic instructions: Run this jar with double click in your file manager or with “java -jar luke-4.2.0.jar” on the command line / bash. Then select the index you need and you are fine to go.