Kotobai+1

Adaptive Japanese practice

Master Japanese with adaptive practice that grows with you.

Practice with thousands of JLPT-aligned questions, each matched to your exact level. Review mistakes, track your progress, and watch your ability grow.

The i+1 approach

Always practicing at exactly the right level

In language acquisition research, "i+1" means the next step just beyond what you already know. It's the sweet spot where learning happens fastest — challenging enough to stretch you, familiar enough to keep you confident. Kotoba i+1 applies this principle to every single question.

Your level, precisely tracked

An Elo-style rating system measures your real ability across question types. Every answer — right or wrong — updates the estimate.

Questions that grow with you

As you improve, the questions get harder. If you struggle, they ease up. Practice always feels productive, never frustrating.

Built for JLPT preparation

Thousands of questions aligned with JLPT N5–N1 covering vocabulary, grammar, reading, and listening. Build the exact skills the exam tests.

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Adaptive difficulty

Every question is matched to your current ability. Answer correctly and they get harder; struggle and they ease up. You're always practicing right at your level.

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Smart error book

Missed questions go straight to your error book. Review them until they stick — then watch them disappear.

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Track your progress

See your ability score trend, daily streaks, and activity heatmap. Pro users get breakdowns by question type.

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Massive JLPT question bank

Thousands of questions across N5 to N1 levels covering vocabulary, grammar, reading, and listening. Always something new to challenge you.

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