Yes, it is. The Conjuring movies are known for being based on the real - life cases of Ed and Lorraine Warren. They were paranormal investigators, and their experiences form the basis for these movies.
The Conjuring 3 is indeed based off a true story. The real - life Warrens were involved in numerous paranormal investigations. Their work was full of unexplained phenomena. In the movie, it tries to recreate some of the aspects of their investigations. It takes elements from their real cases and weaves them into a horror - filled narrative. While it's a movie and there are some fictional elements added for entertainment value, at its core, it has roots in the true stories that the Warrens were a part of.
Yes. The Conjuring series, including the third one, is inspired by true events. The Warrens had a lot of strange cases in their career. For example, they claimed to have encountered various haunted places and possessed people. Their case files were used as the foundation for the story in 'The Conjuring 3'. So, in a sense, it is based on a true story, though some elements might be dramatized for the movie.