This is CLI tool for day-to-day synchronization of kindle books between local directory and directory on device over the wire - using either MTP or old USBMS mount or by using Amazon e-mail delivery.

It was created to support day-to-day side loading usage scenario (based on my multi-year experience owning various Kindle devices):

I have one or more local directories containing books in Kindle-supported formats, possibly organized into subdirectories by authors or genres for easier navigation. I would like to run a single command (not a tool with a UI or additional complexity) from the terminal or console to send these books to my device, while preserving the original directory structure. If there are any additional format specific actions possible (like copying generated page indexes or extracting and copying thumbnails for books) they should be performed transparenly.

Later, I may add new books to the local directories. At the same time, as I finish reading books on the device, they may be removed there. When I run the tool again, I want these changes to be synchronized bidirectionally: new or updated books should be sent to the device, and completed (and deleted) books should be removed locally.

The tool should maintain a history of actions performed. If a book is added to the device outside this process, it should be ignored by the tool and left untouched. Similarly, any additional directories or files created by the device (e.g., Kindle-generated files) should not be affected.