Ask HN: How do services like readwise extract highlights from kindle?

As the question states I want to get my kindle highlights to my personal mail, but it seems to me that there are no public apis to fetch the highlights, and neither does readwise use MyClipping.txt file(I know because it is only present inside the kindle device, and never goes out unless you connect it to your computer). I am wondering how do they do it?

Do they scrape read.amazon.com/notebook, if yes, then wouldn't any changes to the elements of the website break the service and require changes to the readwise approach.

Asking this so that I can write a small script to automate this thingy, and save some money. Any help would be appreciated.