Mastermind Japanese is an adaptive study app for learning Japanese built by Jason Kobayashi. It tracks your progress at the concept level and adjusts practice to what you actually need to work on next.
It is built for busy learners who want structured, practical Japanese study that adapts to how they learn. Current beta scope starts with JLPT N5, with honest progress tracking and concept-level review.
The current beta includes adaptive study with 247 JLPT N5 graph concepts, 688 curated sentence questions, listening-first cards, tap-to-build sentence practice, kanji writing with stroke-order playback, Verb Focus, vocabulary flashcards, private personal decks, and a Mind Map that shows your knowledge structure.
Mastermind tracks concept-level understanding, knows which concepts depend on others, and schedules review based on your actual strength per concept. If you miss a sentence, it isolates the specific concept you need to work on.
Mastermind is officially supported on the latest stable versions of Chrome, Edge, and Safari with a viewport width of at least 360px. Older browser versions, Firefox, Brave, and Android Chrome may work, but are best-effort. The interactive Mind Map renders in 3D and is smoothest with your browser's hardware acceleration enabled (on by default in most browsers); if it looks choppy, turn on hardware/graphics acceleration in your browser settings and restart.
Jason Kobayashi, a software engineer based in Tokyo. He learned Japanese before today’s study apps and internet resources were widely available, using dictionaries, physical flashcards, TV, classes, repetition, and a very overworked electronic dictionary. Mastermind Japanese is his attempt to turn that long-road experience into a more practical way for learners to keep moving.
The current beta is free. After beta, Mastermind will still have a free tier, but its exact content and feature limits are not finalized yet. Current JLPT N5 content is open now.