Where it comes from
NOTE-KU started as a personal discipline: solving every sudoku with notes alone, never writing an answer before the notation proved it. Over time that discipline turned into a system with names and rules — the Notation Pass, the Two-Candidate Rule, Temp Mode, the Final Pass — and the system turned out to be teachable.
The app came next, built to support the method rather than to imitate other sudoku apps: NOTE-KU Mode only lets you place notes until the threshold is reached, the digit bar tells you when a digit is exhausted, Temp notes can never be confused with real ones, and the Final Pass is its own moment.
Why NOTE-KU exists
Millions of people open a sudoku every day 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. It approaches the puzzle from a different direction and uses a single consistent tool from the first move to the last. There is no difficulty level at which the notation approach breaks down: a harder puzzle simply requires more iteration passes, not a different method.
Who it’s for
NOTE-KU is built to be 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 exactly the same notation discipline, just applied across more passes. Nobody needs to switch methods as they get better — they just get faster at the one method.
What we believe
Games can do two very different things with a mind: train it or exploit it. A lot of casual gaming is designed to capture attention. NOTE-KU aims for the opposite — a game that leaves you with something after you put it down: patience, a way of organising information, a habit of proving before acting.
- No guessing. Every puzzle has exactly one solution and can be reached by logic.
- No account. Your progress lives on your device, not on our servers.
- No pay-to-win. Every level is free. Cosmetic themes are earned by solving, not bought.
The method, in one minute
Pick a digit. In every box, find where it can still go. Note it only if it’s down to one or two cells. Follow every consequence, return to the boxes you skipped, repeat. When every empty cell holds exactly one candidate, confirm the whole board in one sweep. If you’re ever stuck, test an assumption — never guess. The full method.
Sudoku and the brain
A 2026 systematic review of brain-imaging studies found that sudoku consistently engages the frontoparietal network — working memory, executive control and error monitoring. The evidence base is still small, and we don’t claim more than it shows; but it’s a good reason to choose a structured, deliberate way to play. What the research says.
What’s available
- The NOTE-KU app — free in your browser, five levels, two modes.
- The Starter Pack — 30 verified, printable puzzles with the method on one page.
- The book series — in preparation, from beginners to advanced, with children’s and teen editions planned.
The three adult books form the written companion to the app. 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 solving. Each book stands on its own.
Where NOTE-KU is headed
The app you can play today is the first piece of a larger project: the full book series, a growing set of themes and digit styles, and native apps for Google Play and the App Store. All of it rests on the same foundation — notation first, guessing never.
Get in touch
Questions, ideas, bug reports, schools interested in the method: contact@note-ku.com. We read every message. More on the contact page.