How it works

The most robust finding in language acquisition is that you acquire a language from input you mostly understand — what Stephen Krashen called comprehensible input, at the level he wrote as i+1: everything you know, plus one step. Most apps approximate this loosely, with leveled articles or curated stories. OptimalChinese takes it literally. The app tracks every word and pattern you know, and every sentence it shows you is generated from exactly that inventory, plus the one thing it is teaching. You never face a wall of unknowns, and you never coast through text with nothing new in it.

That is also why reviews here are sentences, not flashcards. A word alone is a fact; a word inside a sentence you can read is a use. And because sentences are generated, you see a different context on each review — you learn the word, not the card.

Recognizing 图书馆 on a page, catching it by ear, and producing it yourself are three different skills, and being good at one says little about the others. The app treats them as three faces of the word — reading, listening, and production — and schedules each one separately. If your ear lags your eyes, the scheduler simply shows you more listening; nothing else is dragged along.

Spacing reviews out is the other pillar. OptimalChinese schedules with FSRS-6, the modern open-source successor to the twenty-year-old SM-2 algorithm most flashcard apps still run. FSRS models the actual shape of your forgetting and asks for a review just before a word would slip away — fewer reviews, better retention. The app can also fit the scheduler's parameters to your own review history, so the model of your memory is yours, not an average.

Vocabulary follows the HSK 3.0 standard, level by level, ordered inside each level by real-world frequency — the words you will actually meet come first. You can steer by theme, pin what matters to you, and import your existing decks from Anki or Pleco so years of prior study merge into the same schedule instead of starting over.

Taking a class? Your teacher can open a live classroom from a link — no account, no setup — see where you stand, and push words from the lesson straight into your queue.

There are no lives, streak freezes or cartoon guilt. The app shows its working — what is due, why, and what comes next — and gets out of the way. It runs in the browser and as an app, keeps the dictionary on your device so everything opens instantly, and your progress stays in sync across your devices.