EPUB validation the easy way

Do you generate EPUB files?

If you do, you probably already know that before releasing them into the wild it's a good idea to ...

• either validate your individual files
• or validate the output of your EPUB-generating tool

For a long time the International Digital Publishing Forum (IDPF) had a very convenient online validator where you could upload an EPUB. It performed various pre-flight checks and gave very precise details about what was non-standard or broken.

Then the IDPF were merged into the W3C, and sometime afterwards the IDPF validator vanished from the web.

The W3C maintain the underlying tech, but it's written in Java and you need to be a little bit technical to get it going (if anyone is interested they include Docker instructions for it in their Github repo).

For most, it would be much more convenient to have a desktop tool to use. And that's where a company called pagina come in. Over at their website they have a tool called EPUB-Checker.

It is a stand-alone desktop app built around the W3C-owned validation tool already mentioned. It's free and it supports Mac, Windows, and Linux.

I've used the Mac version a fair bit and all the familiar complaints of the old IDPF validator are there. YMMV but very much worth a look.