I looked into this in 2013. At that point there was a "My Clippings.txt" file stored on the kindle that was accessible as a USB storage volume when plugged in. This file stored each annotation in plain text, along with the document ID and the start and ending location of the annotation.
Trouble was, the location was in the Kindle's "Loc" format which is nontrivial (at least to me at the time) to connect to specific text in the document.
I'm sure someone's probably worked this out by now?
Sorry I failed to mention I'm aware of the "clippings.txt" setup, but I would like to be able to have it automated via the web.
Amazon doesn't expose a direct API for highlighting, and Readwise for example does a little "hack" where you use their browser extension to redirect to the Kindle highlights page and I think they just slurp up the authenticated API requests.
There are some books where if you exceed a certain number of highlights, they are not saved on the file anymore, and I’m pretty sure it also affects the web version too.
This is set as part of the DRM, so be careful that you are really saving the data you want. I went deep into a book highlighting things before I noticed this limitation.
Sorry I failed to mention I'm aware of the "clippings.txt" setup, but I would like to be able to have it automated via background API process on the web.
I've been using Readwise (and Reader) which have been great, but it's rather expensive.
I'd love to be able to send an arbitrary article to Feedi like I can with Reader, but also would love to sync highlights back from my kindle.
Going to lurk the repo, cool stuff!