Hello everyone! I'm a solo developer, and intermediate Chinese learner, and I just launched a new Chinese app I want to share with you.

My own Chinese language study stack used to be Pleco (and Goog Translate) for dictionary lookups, and then Anki for flashcard reviews, with a lot of manual copy-pasting in between. Which worked... okay. But the two sides never talked to each other. Pleco doesn't know what I'm studying, and Anki doesn't know anything about Chinese. So it treats 好吃 and 好 as totally unrelated cards, even though getting one right obviously tells you something about the other.

So I built duiduidui! (对对对), which is basically those two tools fused together, with a study engine that actually models how Chinese is structured:

- A dictionary with 200k+ entries, always available/searchable offline (characters, words, phrases, sample sentences, speech audio) where everything is linked. Every character links to the words it appears in, and the radicals it's built from, so you can (for example) go down a rabbit hole exploring the water radical 氵and the characters that contain it (汤 soup, 海 ocean, 河 river, etc). It also includes lots of modern/internet slang entries, not just textbook vocab.

- From the dictionary, you can put any record in your favorites (star collection) and add it to your flashcard deck. Looking something up while watching a show or texting a friend, and then studying it later are all the same workflow.

- Compositional mastery tracking. This is the part I'm most proud of (and that I think the HN crowd will find most interesting): when you correctly review a full sentence like 我喜欢吃猪肉, the system propagates partial "implied evidence" down to 喜欢, 吃, 猪肉, their characters, radicals, etc (weighted by difficulty) and kept deliberately separate from direct evidence. The goal is fewer redundant reviews without the system fooling itself.

- No fixed "learning course". The app keeps an ongoing estimate of your skill-level, and then shows you new material at the frontier of your abilities. But you can always wander off and study whatever you want, driven by your own curiosity or your teacher/class's lesson plan.

Personally, I study with a teacher (on preply), so I designed this app to supplement classes and tutoring, not to replace them. The app even has social features, so you can share your detailed progress with your teacher, and they can see how you're progressing.

The full mathematics behind the study engine are published on our website:

https://duiduidui.app/en/math/

The app uses a Bayesian proficiency model, with kalman filtering (for managing observations in a noisy domain). This is deliberaly not strictly an SRS app, but the card-selection logic is heavily inspired by the ideas of spaced repetition, while managing cognitive load. If you're an SRS nerd, I would genuinely love to hear what you think.

iOS only for now, with paid subscriptions priced at $12.99/mo or $89.99/yr. No ads, no engagement-bait, not based on streaks or other gamified bullshit... Just my own ideas about what would make an awesome Chinese app.

If you try it, I'd love to hear what's confusing, what's missing, etc... And if you just want to argue with my math, that's welcome too. 谢谢!