And for Kindle Previewer (which is what I would recommend):
http://www.amazon.com/gp/feature.html?docId=1000765261
You can use Kindle Previewer to build the book, but that's not what I do. I prefer to upload a validated epub to the Kindle Direct Publishing platform, let it convert there, then download the so-called "mobi" file for previewing in Kindle Previewer and my K3 Keyboard and Fire tablet.