Because the homepage is unavailable anymore.

Original author's note: (c) Lankier. Original license (the same GPLv3) is in COPYING file.

The code requires lxml.

Common python2 ./setup.py build && python2 ./setup.py install will do the job.

But you have to install lxml -- read that page carefully! If you use brew, then you may have to choose pip install or you may have to fix, say, fb2validator.py by inserting something like

import sys; sys.path.append('/where/your/lxml/module/was/installed/to')