About NOTE-KU

A sudoku method, a mobile-friendly app, and an educational book series — built around one idea: systematic candidate notation, applied with discipline, can solve any sudoku puzzle regardless of difficulty.

The app

The app at noteku.app implements the method directly. Players work through the same three phases used throughout the book series — Notation, Elimination, and the Final Pass — supported by visual cues that show exactly when a digit is exhausted and when the completion threshold has been reached.

NOTE-KU is designed to be genuinely playable at every skill level, from a 6×6 Mini grid for newcomers up to Extreme 9×9 puzzles for experienced solvers, using the same notation discipline throughout.

Sudoku and cognitive research

Systematic reviews of neuroimaging studies on sudoku play point to consistent engagement of brain regions responsible for working memory, executive function, and cognitive control — capacities that remain trainable with practice, particularly during high-plasticity developmental years.

NOTE-KU's structured, progressive approach is designed with this in mind, without overstating what the evidence actually shows: the research supports cognitive engagement during play, not guaranteed academic outcomes. We think that distinction matters, and we'd rather be precise about it than make a bigger claim than the science supports.

Why NOTE-KU exists

Sudoku is one of the most widely played logic puzzles in the world. Millions of people open a puzzle every day, stare at a partially filled grid, and begin the same process: look for a number, place it, look for another. It works — until the difficulty climbs past a certain threshold, and the process stops working. The grid resists. The solver stalls.

NOTE-KU exists because there's a better way — not a shortcut, a system. One that approaches the puzzle from a different direction, uses a single consistent tool from the first move to the last, and produces a solving experience distinct enough that players who discover it rarely go back to guessing.

Who it's for

NOTE-KU is built to be genuinely playable at every level. A newcomer can start on the 6×6 Mini grid and learn the Two-Candidate Rule without being overwhelmed. An experienced solver can push into Extreme 9×9 puzzles using the exact same notation discipline, just applied across more iteration passes. Nobody needs to switch methods as they get better — they just get faster at the one method.

The three books

First Marks introduces the method from zero: the grid, the Two-Candidate Rule, and your first guided solves. Narrow It Down adds the Resolution Techniques — Locked Pairs, Locked Triads, the Arrow, and the Grid Read — for intermediate and hard puzzles. The Final Strike covers proof by contradiction and full-board reading for expert-level solving. Each book stands on its own; together, they're the complete written companion to the app. Read the mechanics in full on The Method page.

Where NOTE-KU is headed

The app you can play right now is the first piece of a larger project: the full book series, a growing set of themes and digit styles, and eventually native apps on Google Play and the App Store. All of it is built around the same foundation — notation first, guessing never.