Interesting! I've been thinking about how you'd best teach sentence patterns for a long time, happy someone is making progress on it.
I'm a bit too beginner to effectively use the app, sadly, but it's quite an interesting flow.
As an aside, a while ago, I sort of prototyped the reverse: Learn vocab to understand a natural language sentence, translate the sentence (https://infi.koljasam.com)
Happy to talk and exchange notes, if you want :)
Thanks for your feedback! You can use it as a total beginner too, set your level to hsk 1 and use pinyin. The backend should still give you valuable feedback. I would start learning to form sentences right from the start, it’s more important in Mandarin than in e.g. European languages imo.