The image is of the homepage for
IDPF: The International Digital Publishing Forum
If you decide to distribute your epub through Smashwords, it will get validated, and Smashwords will not list your epub until it passes validation. But the errors they provide are of little help.
You want to run your epub file through a utility called epubcheck to validate it and receive error feedback that’s helpful. There’s an online version available at
IDPF’s EPUB Validator
You can run a version on your desktop by grabbing the Open Source utility epubcheck.jar and installing Java on your computer.
GitHub is a source for the zip file and has a wiki on epubcheck:
For the .zip file:
The main GitHub page for epubcheck:
The wiki starts here:
Okay, so now you’ve got epubcheck.jar. You need Java to run it on your linux or windows or macintosh computer. You’re probably best off googling java download to get the most recent info for your situation.
For Windows 10, the FAQ:
For Macintosh Sierra, the FAQ:
If you’re running Linux, you’re too cool to need my help.
Okay so now you’ve installed Java on your computer.
This gives you the ability to run a .jar file from a command line.
So Windows people bring up the Run command line and enter something like:
java -jar C:/epubcheck/epubcheck.jar C:/test/name of the .epub file
Mac users go into the Utilities folder in Applications, launch Terminal, and . . .
I’ll tell ya. I don’t know what we Mac people do at this point, ’cause this is when I went to the GUI page of the epubcheck wiki:
where I learned about Pagina epub checker:
And here is where I’m at, about to fix the nine errors in my epub file.
What errors? My epub is now valid.
Pagina epub checker gives you the file name and line number of each error, making it easy peasy to fix the problems.
I now have valid epub and mobi files on this site.