The online community "aims to surprise and delight those who have never read a Harry Potter book, as well as returning readers who want to join the conversation", says Pottermore, Rowling's digital publishing arm.
The Harry Potter books have led to a major movie franchise, a sold-out theatre production and multiple theme parks, as well as a booming memorabilia market.
Wizarding legend Harry Potter's tale has turned 20. The White Elephant Cafe, the Edinburgh spot where Rowling wrote the first book, has become an worldwide tourist destination.More news: Young teen falls from ride at Six Flags
Inspired by J.K. Rowling's compelling stories and characters that were brought to life in the Warner Bros. films, "The Wizarding World of Harry Potter" at Universal Studios Hollywood is a masterful recreation, faithful to the visual landscape of the fiction and films, including as its iconic focal point, Hogwarts castle. She's generally known as something of a political firebrand on Twitter, but she was putting the rage aside today by simply tweeting: "20 years ago today a world that I had lived in alone was suddenly open to others".
In October a "Harry Potter: A History of Magic" exhibition will open at the British Library in London, showcasing manuscripts and magical objects alongside Rowling's archives.
"Henry Potter (Harry to his intimates) was a direct descendant of Hardwin and Iolanthe, and served on the Wizengamot from 1913 - 1921", she wrote.
London's St. Paul's Cathedral on Monday published a video of music from the Harry Potter film series being performed at the famous site.