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Basics

How to Play Sudoku

Sudoku is played on a 9×9 grid, split into nine 3×3 boxes. You're given a handful of starting digits, and the goal is to fill in every remaining cell with a number from 1 to 9 — but only one arrangement will satisfy all three rules below at once.

A complete, solved board

Here's what a finished Sudoku actually looks like once every cell is filled in correctly. No blanks, no guessing left — every row, column, and box checks out. The three examples below highlight how, using this exact board.

5
3
4
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9
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The three rules

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Rule 1

Every row has 1–9, once each

Look at the highlighted row. Read across — 4, 2, 6, 8, 5, 3, 7, 9, 1. All nine digits, no repeats. Every row on the board works the same way.

5
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Rule 2

Every column has 1–9, once each

Same rule, reading down instead of across. The highlighted column also contains every digit exactly once — 7, 9, 4, 6, 5, 2, 3, 1, 8.

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Rule 3

Every 3×3 box has 1–9, once each

The grid's nine bold-bordered 3×3 boxes follow the exact same rule as rows and columns. The center box here reads 7, 6, 1, 8, 5, 3, 9, 2, 4.

Puzzle vs. solution

What you actually start with is this same board missing most of its digits — just enough "given" clues left in place to make one, and only one, completed grid possible. Every technique page on this site (Naked Single, Hidden Single, X-Wing, and the rest) shows you how to logically narrow down what belongs in each empty cell, using nothing but these three rules.

Tips

Once you've got the rules down, KaizenDoku teaches you the techniques that make solving faster — and shows you exactly which ones you used after every game.

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Naked SingleHidden SingleNaked PairHidden PairPointing PairsBox Line ReductionX-WingSwordfishUnique Rectangle