How to play NOTE-KU

Getting started

Open noteku.app/play in any modern browser on a phone, tablet or computer. There is no download and no account. After a short splash screen you land on the main menu as Player; you can change your name any time in Settings › Preferences (up to 20 characters).

Modes and levels

Choose a mode first:

• NOTE-KU Mode (recommended) — you can only place notes until every empty cell holds exactly one correct candidate. Then the Final Pass unlocks and you confirm the board.
• Classic Mode — standard sudoku: place digits directly, with full note support. Apply the method at your own pace.

Then choose a level. Every game generates a fresh puzzle, checks that it has exactly one solution and that it can be solved by logic alone.

Level	Grid	What to expect
★☆☆☆☆ Mini	6×6	Digits 1–6, boxes of 2×3. The best way to learn the rhythm. Practice mode: no NoteCoins.
★★☆☆☆ Beginner	9×9	Many givens. Your first full Notation Pass.
★★★☆☆ Intermediate	9×9	Two or three passes; cascades start to matter.
★★★★☆ Advanced	9×9	Fewer givens, more skipped boxes, longer iteration.
★★★★★ Extreme	9×9	The fewest givens. Every elimination counts.

The game screen

• Header — ‹ BACK returns to the level list (your puzzle stays available to resume while the app is open). On the right: 💡 AI Guide (coming in a future update), ⚙ Settings, and ? a quick reference of the method.
• Info bar — difficulty stars, the timer, the mode, and an orange ⚠ counter if you make errors.
• Phase banner — tells you where you are: Notation Phase, Threshold met or Final Pass.
• The grid, then the action bar (Undo, Erase, Temp) and the digit bar (1–9, or 1–6 in Mini).

Placing notes

1. Select a digit in the digit bar. Every cell already holding that digit, and every note of it, is highlighted.
2. Tap an empty cell to add that digit as a note. Tap again to remove it.
3. Swipe across several cells to note (or un-note) the digit in all of them in one stroke.

Each cell holds up to three notes. Under the Two-Candidate Rule you rarely need more. Tapping a given number on the board is a quick way to select its digit.

Undo, Erase and Temp

Button	Tap	Hold (about 0.7 s)
↩ Undo	Steps back one move.	Keeps rewinding your moves in reverse order, faster the longer you hold. Let go to stop exactly where you want.
Erase	Turns eraser mode on or off. While it’s on, tap or swipe cells to clear them.	Clears every note on the board so you can start the puzzle over. Givens are never touched, and a single Undo tap brings everything back.
Temp	Turns Temp Mode on or off.	—

A thin bar fills along the bottom of Undo and Erase while you hold, so you can see the hold coming before it triggers. Both use the same hold time.

Temp Mode

With ●TEMP on, new notes are temporary: they appear on a contrasting colour that every theme keeps distinct from permanent notes. Use them to test an assumption (how).

Shortcut for the classic test: if a box has exactly two permanent notes for the selected digit, tapping one of those cells in Temp Mode lifts both notes and places a temporary note in the cell you tapped — you’re now testing that option. CLEAR removes every temporary note at once; Undo brings back the two original notes.

The digit bar: NOTED and DONE

• ✓ NOTED — the digit is exhausted for this pass: every box either holds it, has one or two notes for it, or still has three or more open cells. Nothing more to do with that digit right now; move to the next. (You can hide these badges in Settings.)
• ✓ DONE — every instance of the digit is confirmed on the board.

Threshold and the Final Pass

When every empty cell holds exactly one note and every note is correct, the banner announces THRESHOLD REACHED and a ⚡ BEGIN FINAL PASS button appears.

In the Final Pass, select a digit and tap each cell whose single candidate is that digit; a small dot marks the cells ready for the selected digit, and a counter shows how many cells remain. Undo, Erase and Temp are put away: the work is done, this is the confirmation.

When the last cell is confirmed you’ll see your time, your errors and the NoteCoins you earned.

Classic Mode

With NOTES OFF, tapping a cell places the selected digit (tap again to remove it). Switch to NOTES ON to pencil in candidates instead. Two settings help here: Smart Error Detection marks a digit that doesn’t match the puzzle’s solution, and Auto-remove Notes clears that digit’s notes from the row, column and box when you place a correct answer.

Create your own puzzle

At the bottom of the level list, Create Your Own Puzzle lets you type in any 9×9 puzzle from a book, newspaper or website. Enter at least 17 givens and tap Check & Play. The app rejects duplicates, then verifies the puzzle has exactly one solution before you start.

NoteCoins and the Store

Solving earns NoteCoins (₦), the app’s virtual currency. They have no monetary value and can’t be bought; you spend them in the Store on themes and digit styles.

Level	Base reward
Mini 6×6	Practice — no coins
Beginner	₦10
Intermediate	₦20
Advanced	₦50
Extreme	₦100
Your own puzzle	₦10

Zero errors multiplies the reward by 1.5; three or more errors halves it. Light and Dark themes and the classic 1–9 digits are free forever; 23 more themes (including nine country themes) and 25 digit styles — Roman numerals, world currencies, fruits, animals, flags, moon phases and more — unlock in the Store.

Settings

Styles: theme and digit style (locked items show 🔒 until you own them).

Preferences: player name · Show Timer · Countdown Mode (with your own time limit) · Highlight Region (row, column and box of the selected cell) · Show Noted Badges · Smart Error Detection · Auto-remove Notes. Your choices are remembered on this device.

Your progress and privacy

Your name, NoteCoins, purchases, theme and settings are saved in your browser on your own device — nothing is sent to a server and there is no account. That also means progress doesn’t move between browsers or devices, so stick to one browser. A puzzle in progress stays available while the app is open; closing or reloading the page starts fresh. Details in the privacy policy.

Add NOTE-KU to your home screen

On Android, open noteku.app/play, tap your browser’s menu and choose Add to Home screen or Install app. On iPhone and iPad, tap the Share button in Safari and choose Add to Home Screen. NOTE-KU then opens from its own icon like any other app.