The output produced by GPT is mostly on point. However, it does makeup stuff sometimes. A fine-tuned or smaller model trained on music theory data is the way to go in the future. Your app sounds interesting. Please share whenever you can!
This app is a hobby project and is in the initial phases. I removed the option for chords like m7b5 in the UI for now. I will re-enable it when I finish performing tests on GPT-4's response.