When I’m reading on my Kindle, I can export my notes to JSON using my Chrome Extension, AmaJSON. I love being able to share / search / re-use notes that I store in JSON (example).
I made bn.stevengharms.com to help out.
It helps you build a valid JSON file that contains all your annotations. Use buttons to inject good chunks of JSON, fill them out, inject again.
The app backs up your progress within your local browser so you won’t lose work if should accidentally refresh. It’s simple and lightweight and not supported, not tested, not anything special.