Adobe EpubCheck 0.9.1 is a Java-based command-line tool
to validate IDF Epub files. It can be used to detect various types of errors in an Epub OCF container structure and in OPF and OPS mark-up, and to check for internal reference consistency. While this tool is probably not for your average joe, early adopter Epub geeks may find some use for it.
Now this tool (named EpubCheck) is available as an Open Source project. It is not complete (there are still many checks that we can do), but it is already fairly mature and extremely handy. If you author epub files, you should consider running this tool on your content regularly.
[via Adobe Digital Editions blog