QualityCheck Plugin Hack (Stop Amazon from deleting your sideloaded books)

Last updated: 2026 / 01 / 16
taken from a rentry.co page on mobilereads, for archival purposes

Reports suggest that Kindles may delete all sideloaded books after a prolonged use of Airplane Mode due to an internal labeling bug with Calibre. If you have used Calibre to send books to your Kindle, you might have noticed that these books are labeled as purchased books instead of personal documents. More specifically, they appear in the Books category rather than the Documents category.

When the Kindle reconnects to Wi-Fi, it checks for an internal purchased label within the sideloaded books, and since it cannot confirm whether that book is legit, it confuses itself and decides in deletion.

Some reports suggest that tagging these sideloaded books as PDOC (Personal Document) instead of the default EBOK may circumvent this problem.

The issue lies mostly with Calibre, as it still tags sideloaded books as EBOK and still does not offer a way to change this for AZW3 sideloaded books. We have to tag every book as PDOC before sideloading them to your Kindle.

If you're using KFX or MOBI for your sidelaoded books, you might want to skip to the FAQ.

AZW3

1. Download and install the QualityCheck plugin within Calibre (Preferences > Advanced > Plugins > Get New Plugins)
2. Go to your Calibre Plugins folder (C:\Users\user\AppData\Roaming\calibre\plugins)
3. Unzip the qualitycheck.zip plugin as a folder
4. Search for a file named check_fix.py
5. Modify the following lines with any text editor:

  mu.update(asin, b'EBOK')  

to...

  mu.update(asin, b'PDOC') 

1. Save changes, select all the files inside the folder and zip them. Do not just zip the folder, that will just make a zip with a singular folder inside and it will not be detected as a plugin on Calibre
2. Replace the old QualityCheck.zip file
3. In calibre, convert any book to AZW3
4. Open the QualityCheck plugin > Fix > Fix ASIN for Kindle Fire.
5. Your AZW3 book is now a PDOC.

You can use any metadata viewer to see if the book is actually a PDOC.

MOBI/KFX

MOBI converted books are tagged as PDOC by default, if unsure check on Calibre Preferences > Output Options > MOBI.

For KFX books (created with the KFX Output plugin), you can tell Calibre to always tag converted books as PDOC. (Calibre Preferences > Output Options > KFX Output > "Create personal document").

F.A.Q

Can this be automated?

You can automate this process of Converting to AZW3 and sending them to Kindle with the Actions plugin.

Is this method safe? Will something happen to my Kindle?

Yes it is safe, nothing bad will happen to your Kindle. There haven't been reports of PDOC tagged books being nuked so far, here is one report claiming their PDOC tags weren’t nuked.

But why not just use Send To Kindle? isn't that easier?

Some people prefer to keep their Calibre library synced to the Kindle.