https://www.vice.com/en_us/article/88avkp/this-simple-tool-will-help-you-see-what-websites-know-about-you

Big tech knows a lot about us, and finding out exactly what it knows and downloading a copy of it can be a chore. JustGetMyData is a website that helps users navigate sites like Facebook and Twitter so they can download a copy of their data and see what, exactly, our favorite websites know about us.

JustGetMyData is a fork of JustDeleteMe—a website that helps users navigate the often complicated process of scrubbing themselves from sites like Instagram.. Amazon makes it easy to return a defective product through a series of menus, but if you want to delete your account you’ll have to call someone, for example. Retrieving a copy of your personal data can be a similarly complicated process, but JustGetMyData makes it a little easier. And, if you’re planning to delete these accounts, it’s a good idea to get a copy of your data first.