If you’re publishing on Kindle, chances are you want your book to look good on it. But that may require a task not usually performed by Kindle authors: testing your ebook thoroughly.
No, it’s not always enough to check your Kindle book in Amazon’s online previewer—and even if you pay someone to convert it, they may miss a problem your readers won’t. This article will survey the tools and procedures for finding such problems yourself.
Originally, the chief difficulty of formatting for the Kindle came from its substandard, deficient ebook format. Nowadays, the chief problem is that there is no one Kindle. There are several families of Kindle, both hardware and software, with a variety of members in each family, and more than one basic format spread across them.
Families include e‑ink Kindles (Kindle, Kindle Keyboard, Kindle DX, Kindle Touch, Kindle Paperwhite), tablets (Fire, Fire HD, Fire HDX), mobile apps (for iOS, Android, Windows 8, Blackberry), desktop apps (for PC and Mac), and even a “Cloud Reader” for browsers. The Kindle also has two completely different formats for its books: the older Mobipocket format (MOBI) and the newer Kindle Format 8 (KF8). Though only one format will be delivered to each customer’s Kindle, both formats are included in your preview files.
This broad diversity in the Kindle family is coupled with the fact that Amazon engineers who work on Kindle don’t seem to care much about consistency or fixing past errors. They’re constantly moving on to new Kindle platforms and initiatives without fixing reported errors or reconciling differences with the old. And so they leave behind a tangle of quirks and incompatibilities that rivals anything from the worst days of the browser wars.
Thorough testing, though a limited defense, is the only one we have.
Once you’ve signed up for an account there, you can also start the setup for your book title. That lets you upload and convert your files any number of times for testing before you’re ready to publish.
You can even set up a book title you never intend to publish, and use it to test any book or to just experiment. At this writing, for example, the titles on my KDP Bookshelf include Test and Test 2. They allow me to test new versions of a book already published without disturbing the finished files I’ve submitted earlier or taking the chance I’ll release a draft by mistake.
Upload and conversion normally take only a minute or two. And since this is also the method you’ll use for final submission, you know you’re getting the most reliable result possible.
When your book is ready, you can click “Preview book” to see it in KDP’s online previewer. This provides a convenient way to check content, and you can set it to emulate various Kindles.
In its current version, this previewer has improved quite a bit in accuracy, but it is still slow. Also, it is not good for judging picture quality, since it is actually showing a highly compressed JPEG image of each page.
Proofing on the Desktop
After conversion, Amazon KDP will also offer the option of downloading your book as well as a previewer to run on either Windows or Mac. Though not perfect, this Kindle Previewer provides the best possible look at your book without seeing it on actual Kindles. The Previewer can also be downloaded here:
When you launch the Previewer, it opens a home window with option settings, helpful links, and Amazon announcements—including notice of Previewer updates. You can open your book through the File menu, but you can also just drag and drop it on this window. To get multiple preview windows for comparisons, just launch the Previewer more than once.
As with the online previewer, you can choose among several Kindle models to emulate, selecting from the Devices menu for Kindle families, then from the top tabs for individual models. You can test both external links and internal navigation, and change settings where applicable for screen orientation, font size, font face, and color mode—Normal, Night, and Sepia. To spot problems, you should test as many combinations of device and settings as practical.
At the same time Amazon has extended its Kindle Format 8 to older Kindles, it has also removed options to test the Mobipocket format in the Previewer. At this point, only the first two generations of Kindle still use Mobipocket, and of the Kindles in those generations, only Kindle DX can be chosen as a device in the Previewer.
As valuable as the Kindle Previewer is for previewing, it has another, less‑known capability worth almost as much: It can be used to convert your HTML file to a Kindle book! Amazon’s Kindle converter is built right into the Previewer. All you need do is open or drag in your HTML file, and the Previewer will handle the rest.
The conversion provided by the Previewer is not quite as good as the one you get at Amazon KDP. Specifically, it will be missing your cover, as well as menu items for the book’s “beginning” and table of contents. Still, combined converting and previewing in the Previewer lets you run quick and mostly accurate tests of formatting without the need to visit Amazon KDP and wait for processing.
Another advantage of converting in the Previewer is that you get access to a log of what Amazon calls “Compilation Details,” including warnings and error messages. These can be valuable in pinpointing errors in your files or in just studying how the converter operates.
The Kindle converter—formally called KindleGen—is also available on its own, for use on Windows, Mac, and Linux. Direct use of KindleGen is too geeky to discuss in this article, but if you like, you can find the program here:
You may have trouble starting the Kindle Previewer if you are on an older, 32‑bit computer running Windows 7 or Vista. In that case, Amazon advises you to set the Previewer’s compatibility mode to “Windows XP (Service Pack 3).” To do this, right‑click on the Previewer shortcut in your Start menu, click on “Properties,” and go to the Compatibility tab.
Other problems may arise because the Previewer, instead of running directly on Windows and Mac OS, relies on a cross-platform system add‑in called Java. Problems with the Previewer may stem from incompatibility with the Java version on your computer, possibly resulting from Java updates. At one point, for instance, the Previewer worked on the Mac only with Java 6—the last version issued by Apple itself—while failing with Java 7—a version more up-to-date but issued by another source.
By default, the newest versions of OS X don’t include Java at all. But they should prompt you to download and install it when needed.
On the Mac, the Kindle Previewer’s Paperwhite emulation relies not only on Java but also on an archaic system add‑in called X11, which any commercial software developer would be ashamed to require. If you don’t already have this on your computer, the Previewer is supposed to prompt you to install it. You can then download and install XQuartz, the X11 version that comes from an independent source but is supported by Apple. Find it at
To make it work after installation, you’ll have to log out or restart and also consent to allow “webreader” to accept incoming network connections.
The problem is, you may not get a prompt if X11 is already in your system but in an older, incomplete, or incompatible version. The Previewer may then open but go into an endless round of error messages when you try to view your Kindle book on Paperwhite. And it doesn’t help that Paperwhite is the Previewer’s default for initial display of your book. (Luckily, you can at least change that default from the home window.)
If you run into such trouble, your first step is to uninstall each of the following two folders that may be in your usr folder.
Don’t know where the usr folder is? It’s at the root of your primary hard drive or partition, along with Applications and System—but, of course, it’s invisible. So, to get to the folders inside usr, you must have a utility that makes all your hidden files and folders visible, or else use this command in your Terminal utility to delete the folders while still hidden:
sudo rm -rf /usr/X11/ /usr/X11R6/
Note that Terminal won’t show your password when you type it to authorize the operation, and it also won’t tell you the folders are deleted. You’ll just see a new prompt. You can then install XQuartz.
Even when XQuartz is working, you’re not entirely in the clear, because a security update to Mac OS or Java may cause it to fail. The times this happened to me, I was able to fix it by reinstalling the same version of XQuartz.
If you’re a Mac user and get really desperate, you might consider running the Windows version of the Previewer in a Windows emulator like VMWare Fusion. Then again, you might have trouble there too!
One limitation of the Kindle Previewer is that current versions will no longer emulate Kindle for iOS. If you select iPad or iPhone, the Previewer will instead generate a special file you can load onto those devices and preview there. I’ll cover that in the next section.
Proofing on Kindles
If your Kindle book works well on the Kindle Previewer, it’s more than likely to work well on actual Kindles. Still, it should be obvious that the ultimate test is to try it on the Kindles themselves. (And sometimes you may find that a problem with your book exists only on the Previewer!)
Of course, no one expects you to have access to every single Kindle model. But almost anyone can view their book on one or more.
You can start with one of the free desktop Kindles for Windows or Mac, available here:
Once installed, these apps will open your book automatically when you just double-click it.
The tricky part, though, is that the app will also add the book to your desktop Kindle Library, which you access through the app. The next time you double-click that book on your desktop, or even just a book with the same file name, it’s the copy already in your Library that you’ll see. To make a newer version open instead, you’ll have to either make sure the new file has a different name or else delete the old version from the Library. (If you convert with the Kindle Previewer, it automatically gives your book file a unique name.)
You may already have one or more of Amazon’s hardware Kindles for your own reading. On the other hand, I’m often surprised to find people wanting to publish on Kindle who don’t own or use one themselves and may never even have held one.
Kindles are now cheap enough so that, if you’re serious about Kindle publishing, there’s seldom a reason you can’t own one or more just for testing. For my own tests, I have one Kindle from each major family—a late-generation basic Kindle, a Kindle Paperwhite, and a 7‑inch Kindle Fire HD. All together, they cost no more than a single Adobe publishing app!
To get your Kindle book onto most hardware Kindles, all you need do is connect the Kindle to your computer with the USB cable you use for charging, or one like it—one with a micro USB plug, for all but the oldest Kindles. In the Kindle’s directory, you should see a “documents” folder where you can drop your book. The tablets, though, are more complicated and vary from model to model, so refer to your user’s guide or search online for instructions.
As an alternative, you can send your book to your Kindle—not by email, which reportedly strips out advanced features, but with one of Amazon’s Send to Kindle desktop applications, available for Windows or Mac. Find them here:
These apps upload the file to Amazon, which turns around and sends it back to selected Kindles via Wi‑Fi or Whispernet, the Kindle’s cellular network. In most cases, you’ll want to tell the app not to archive the document in your online Kindle library. Along with that, make sure your destination Kindle is set to show what’s on your device, not in the Cloud. Also note that, for a Kindle Fire, your book will wind up in the Docs section rather than under Books.
Besides the desktop and hardware Kindles, you have the Kindle apps for other mobile platforms. These platforms currently include Apple’s iOS—for iPad and iPhone—Google’s Android, Microsoft Windows, and the BlackBerry OS.
Send to Kindle can be used with these, too, with the books showing up under Docs. But on the iPad or iPhone, you’ll then be viewing your book in the older Mobipocket format instead of the newer Kindle Format 8, as you should be.
To view your book properly on iPad or iPhone, you’ll need a special file produced by the desktop Kindle Previewer (version 2.91 or later). Open your book in the Previewer and use the Devices menu to switch to Kindle for iOS. The Previewer will then automatically create a file with the extension .azk and provide a link to its folder, if you need that.
Unfortunately, Send to Kindle won’t handle this file, so you’ll have to transfer it with iTunes instead. Here are the steps:
1. On the iPad or iPhone, exit the Kindle app if you are in it. (It may also help to shut down the app entirely, though that’s not supposed to be necessary.)
2. Connect the iPad or iPhone via its charging cord to your computer’s USB.
3. Open iTunes on your computer.
4. Select your iPad or iPhone from the items in the sidebar. (If you don’t see the sidebar, choose to show it from the View menu.)
5. Select the Apps tab (at the top, not in the sidebar).
6. Under File Sharing, choose Kindle.
7. Import your book by clicking the Add button, or just drag it into the Kindle Documents area. (Weirdly, there’s no command within iTunes to remove a document from the list, but you can just select it and press Delete on your keyboard.)
8. On your iPad or iPhone, enter the Kindle app.
9. Wait a minute or two. The book should disappear from the Kindle Documents area on your computer and appear on your iPad or iPhone.
With this method, your book will show up among other Books on the device—not in the Cloud. (It might not appear in correct alphabetical order.) The Kindle app will then be able to display it properly. To remove it later, simply delete the book from within the Kindle app—not with iTunes.
Unpacking your Kindle book is an optional procedure that takes apart the preview book package so you can inspect its component files. It’s particularly useful for checking on how the Kindle converter has processed your pictures. It can also be used in troubleshooting your book’s formatting and navigation, if you’re familiar enough with HTML.
If you know much about EPUB—the rival ebook format to the Kindle—you probably know it’s actually a collection of files in a Zip archive. That makes it easy to take apart and put back together. A Kindle book too is a collection of files, but packaged in a less common format—a Python database. To take it apart, you need a utility called KindleUnpack (formerly MobiUnpack). It can be downloaded from the first post in this forum thread:
KindleUnpack requires some version of the Python software language to be installed on your computer. Macs already have it. For Windows, you can download free versions from either of these locations, among others:
You want version 2.7 or later—but not Python 3, a complete overhaul that is incompatible with many existing scripts.
What you’ll see after unpacking includes the source files you fed the converter plus files and folders for two different versions of your Kindle book—the Kindle’s old Mobipocket format (here called “mobi7”) and the newer Kindle Format 8 (here called “mobi8”). Each of these versions will have its own HTML file for the book contents, and its own set of image files. Note that, in the preview before unpacking, only a single set of images is shared by both formats, but KindleUnpack duplicates them for your convenience.
Unfortunately, the final testing of your book can come only after you publish it. That’s because KDP staff may alter it before letting it go on sale! Most commonly, if you’ve inserted a “start” guide item, they will move it if they think the book should open in a different place—and they’ll never tell you they did it. So, if you want to be absolutely sure of your book, be prepared to buy or borrow a copy.
But that’s not the end of it. If you later revise and resubmit your book and then want to check it again, you’ll have to jump through yet another hoop.
To safeguard customers’ notes within a Kindle book, Amazon won’t automatically update purchased copies of the book when you submit a new file. No matter how many times you delete the book from your Kindle and redownload, you’ll keep getting the old version. It no longer helps even to entirely remove the book from your account and buy it again!
If you ask Amazon KDP to make your update available to all past purchasers, they may offer that option after a review that can take up to four weeks. (They may also use the opportunity to insist on questionable changes to your formatting—which is why I’ve stopped making such requests.) Short of that, the only way for you to get the update yourself is to contact Amazon Customer Service and request the replacement of your personal copy with the new version.
And if it turns out that KDP staff has improperly placed the “start” or made another objectionable change? You can contact them and ask them to fix it. Or else resubmit the file in another roll of the dice. And then, of course, retest.