Mastermind is built around one idea: model what you actually know, honestly. Here is how that works — and how you can check it yourself.
It records everything, and never forgets
Every answer you give — questions, flashcards, listening, speaking, writing — is recorded permanently in your personal study ledger. Nothing is averaged away or overwritten. From that history, the brain maintains a belief about each concept you've met: how strong it is, and how fast it's fading. Yes, fading — the brain models real memory decay, because your knowledge is a garden, not a trophy case.
It chooses every card for a reason — and tells you
When you study, every candidate item is scored: is a review due? Is something you knew starting to fade? Are you ready for new material? Did you ask to focus somewhere? The highest-scoring item wins. No fixed lesson order, no random shuffle. And you don't have to take that on faith — tap "Why this now?" on a question card and the brain states its reason.
It grades its own predictions
A brain that models you should be able to predict you. Before a mock exam starts, Mastermind locks in its expectations — and after you finish, it shows you the receipt: "we expected about N correct; you got M," section by section, including where it was overconfident. We measure our prediction quality continuously and use the misses to improve the model. Few learning apps will show you when they were wrong; we think that's exactly what earns trust.
What it deliberately does not do
No guilt streaks, no loss-shaming mascots, no dark patterns — if you come back after two weeks away, the brain simply recalculates what's worth reviewing and gets to work. And honest limits: Mastermind is in beta, currently focused on JLPT N5, and adaptation is statistics, not magic — it needs a few sessions of evidence before its picture of you is sharp.
Your data is yours
Speech recognition for speaking practice runs on your device — your voice never leaves it. Your full learning history is downloadable from Settings as a single file, and account deletion is real deletion, including cleaning up payment-provider records. No third-party analytics, no ad trackers.
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