"This is such a great way to give something back to the fans who made Harry Potter such a huge success," she said.
Pottermore.com will also feature games, forums and other snippets of new material for fans to pour over.
"Most of this writing is material I generated while I was writing the books initially," explained JKR. "It's background, and lots of details that didn't make it into the books."
The author also confirmed that there are no plans for an eighth Harry Potter novel.
Pottermore will officially launch on July 31st (which dedicated fans will tell you is Harry Potter's birthday...)