Pressbooks helps you create high quality ebooks that meet the industry standards set by the International Digital Publishing Forum (IDPF) and submission requirements of all mainstream ebook retail platforms. Supported ebook formats on Pressbooks include EPUB 2 and MOBI. EPUB 3 files are also available in beta format.
Before you submit your ebook files for publication, we highly recommend testing your files on a few common ebook platforms. Read on for a list of recommended ebook testing tools.
Free Ebook Testing Tools
The ugly non-secret of ebooks is that they look different on just about every platform. No matter whether its Kindle or iBooks or Nook or Kobo or some other reading platform, you should expect some variation in the reading experience. Pressbooks works hard to standardize the design of your ebooks, but if you want to know exactly how your book will look after it’s available for purchase, we suggest downloading your ebook files and viewing them on a few of the free ebook reading tools listed below.
- Adobe Digital Editions
ADE is Adobe’s free desktop EPUB reader. Since ADE was one of the first widely accepted ebook-reading technologies available, it’s used to power a lot of different services’ ebook platforms. How your book looks on ADE is a good indicator of how it will look elsewhere.
- Kindle Previewer
Amazon Kindle requires that ebooks are created in their own proprietary format: MOBI. Likewise, the MOBI format is only compatible with one testing tool: Kindle Previewer. If you’re testing your MOBI files, Kindle Previewer can show you what your ebook will look like in tablet, phone, or ereader format. It also allows you to modify the display with the same settings available on the Kindle ereader software. NOTE: We do not recommend uploading your MOBI files from your desktop directly to your Kindle or Kindle mobile app. See more information below.
- Apple Books
Apple Books is an ebook reading application available on all iPhones by default. It can also be used to read ebooks on MacBook computers, on iPads, and on the iPod Touch. This software is free, but can only be downloaded if you have an Apple device.
- Rakuten Kobo
Kobo is another common ebook reader. You can download the Kobo application on your phone to view your EPUB files. It’s also possible to transfer your EPUB files directly from your desktop to your Kobo device.
Dropbox is a great tool to let you access files from multiple devices — drop your EPUB file into a folder in dropbox, and then you can access it from any device.
- IDPF Validator
The International Digital Publishing Forum maintains a tool that allows you to “validate” your EPUB, or make sure that the file conforms to globally accepted standards and specifications required by all ebook platforms. EPUB files with validation errors may be rejected from ebook retailers, which is why we recommend either testing your files with IDPF or enabling Pressbooks error reports before you submit your files for publication. Read on for more details.
Testing MOBI Files on Your Apple Device
If you try to upload your MOBI file directly to your iPhone or iPad, what you see probably won’t look very good. However, that same file sold through the Amazon Kindle bookstore will look the way you designed it. This is why we don’t recommend testing MOBI files on any software other than Kindle Previewer: results can be misleading if files aren’t viewed the right way.
Pressbooks uses Amazon’s Kindlegen software to create a MOBI file from the original EPUB file. Since Amazon created the MOBI format and is the only distribution service that uses it, the tools and devices that can be used to view a MOBI format are entirely controlled by Amazon and are fairly limited when compared with the EPUB format.
In addition, the process of creating a MOBI file actually involves bundling two files together: a KF8 file and a MOBI7 file.
The KF8 file is used in all modern Kindle applications and devices, with the exception of devices running Apple iOS.
The MOBI7 file is used only on outdated Kindle e-ink devices; it’s a very limited format and doesn’t support many of the styles offered in Pressbooks.
Now, you’re wondering: if KF8 doesn’t work for iOS, and MOBI7 files are limited, what happens to ebooks on Apple devices?
The answer is that when you submit your MOBI file to Kindle, they create a third proprietary file format called AZK. Since AZK files aren’t generated by Kindlegen, they can’t packaged with your original MOBI file when it’s exported from Pressbooks. This means your MOBI file won’t be compatible with iOS devices until it’s been uploaded and sold through Kindle. Uploading your MOBI file to an IPad or iPhone will show you the MOBI7 file we described above, which means only basic styling will be visible.
The AZK version of your ebook should look the same as the KF8 version of your ebook, which is the version you’ll see when you upload your file to Kindle Previewer.
Ebook Validation Logs & Error Reports
There’s a difference between testing your ebooks for design and testing them for functionality. The majority of the tools listed above will help you test for design. You can use them to see what your ebook will look like on distributor platforms and get a pretty good idea of the reading experience your book will offer. When testing on Kindle Previewer, or Apple Books, or Adobe Digital Editions, you’ll want to keep an eye on things like fonts, colors, and margins.
Testing for functionality involves making sure that your book meets all the technical specifications required for submission to distribution services. That means that all the correct metadata has been included, that there aren’t issues with how your images have been embedded, and that all your internal links have been set up correctly.
By default, ebooks created on Pressbooks are built to conform to these specifications. However, the content that you import into Pressbooks may introduce validation errors that Pressbooks is unable to resolve automatically.
The last of the tools listed above, the IDPF Validator, does help you test your EPUB files for functionality. You can also receive error reports from Pressbooks automatically by following these steps:
- Go to Settings > Export from the left sidebar menu of your book’s dashboard
- Find the Email Validation Logs setting and change it from “No. Ignore validation errors” to “Yes. Email me validation error logs on export”
- Click Save Changes
Pressbooks will then scan your files for validation errors every time you export a fresh set. If a validation error is found, the error will be flagged on the export screen, and a report will be sent to the email associated with your Pressbooks account. If you need help figuring out what the error report says, check out our Validation Logs chapter.