Testing Pressbooks’ Kindle Output on iPhones and iPads (MOBI7, KF8, AZK, gahhh)

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If you test your Pressbooks output of Kindle files on your iPad/iPhone, it will look not look very nice. But the files that people actually buy from Kindle on iOS devices will look fine.

Here is why:

Pressbooks uses Amazon’s Kindlegen software to create the MOBI export (which converts from the EPUB file generated by Pressbooks). This actually creates 2 files, a KF8 file and a MOBI7 file, bundled together as one MOBI file.

KF8 file

  • KF8 file format is used in: Kindle Fire, Kindle Android apps, and Kindle’s “modern” eink devices: Paperwhite et. al.
  • the KF8 file is really an EPUB with a couple of modifications … and uses the same styling technology, CSS
  • NOTE: the KF8 file is NOT used in iOS devices (iPhone, iPad), however … see below*:

A MOBI7 file

  • MOBI7 format is used in OLD Kindle eink devices
  • MOBI7 is a a VERY limited format (for instance, no background shading, very limited support for styling, and no support for CSS )

Because of the constraints of MOBI7 styling, in Pressbooks, we swap out all the nice styling from our EPUB/KF8 formats for a generic “try your best not to look like total crap” output … which is all you can hope for on old eink Kindles.

BUT…What about iOS? (.AZK)

  • When a user buys a Kindle book from Amazon, on an iOS device (iPhone, iPad), Kindle actually delivers a third format: .AZK
  • The .AZK file on the iPhone/iPad looks more or less like the KF8 file in Kindle Fire, which is more or less what the EPUB looks like in iBooks.
  • The .AZK file is generated by Amazon, at some point between when you upload your ebook files to Kindle, and when the user buys and downloads the book from the Kindle  store
  • .AZK files are NOT generated by Kindlegen (hence not from Pressbooks) … when you create a MOBI file

However Testing MOBI output on iPad/iPhone … displays .MOBI7 not .AZK

  • If you sideload (ie send a MOBI file to your iphone/ipad and open it, without buying from Kindle) … it displays the MOBI7 file (see above), which will look “as uncrap as we can make it” …
  • This doesn’t look nearly as nice as your book looks when testing on Paperwhite, or Kindle Fire
  • BUT: it is not what buyers of your book on iOS devices will see either!

To see what your book will actually look like to Kindle buyers on iOS devices, you need to upload your book to Kindle and actually make a purchase on iOS.


So, all that to say:

  • Testing your Pressbooks output on your iPhone Kindle is going to look like crap
  • What readers will actually see when they buy from Kindle on their iOS device will look like the KF8/Kindle Fire output … which should look nice.


A couple of fellow masochists from the world of ebook production rightly point out on Twitter that you can indeed test the AZK file on your Kindle/iOS, here is how:

  1. download Kindle Preview software (free)
  2. upload your MOBI file to Kindle Preview
  3. from the top menu, select: Devices –> Kindle for iOS
  4. this will convert the file to .AZK … and give you a link to the file on your computer
  5. take this file, and add it to your iTunes library
  6. connect your iOS device to your computer via USB
  7. go to Add Files … and select the .AZK file to transfer to your device
  8. open the Kindle app on your device, and look at the file
  9. in theory, it should look nice.

Eaaasy as pie!