How to Play Sudoku
Sudoku is a game of pure logic. No arithmetic, no trivia, no luck: just a grid, nine digits and three rules. This page covers everything you need to start — and where to go next.
The goal — and the sudoku rules
The grid is a square of 81 cells: nine rows, nine columns, nine 3×3 boxes. Some cells are filled at the start: these are the clues, or givens, and they never change. Your goal is to fill every empty cell with the digits 1 to 9 while respecting the rules. A well-made puzzle — and every puzzle here is — has exactly one solution, reachable by reasoning alone.
Each digit from 1 to 9 must appear exactly once:
- in every row;
- in every column;
- in every 3×3 box.
That's all. Every cell belongs to a row, a column and a box at the same time, and must satisfy all three constraints at once. The whole game grows out of that overlap.
Where to start: scanning
Don't start with a random cell. Start with the digits that already appear most on the grid: if there are six 7s placed, only three are missing, and the constraints on them are already tight. Pick a digit, look at where it sits, and ask, box by box: which cells can still take it? When the answer is "only one", you have your first move.
This systematic read is called scanning, and it's the foundation of everything: at the entry levels it's enough, on its own, to finish the puzzle. Easy sudoku is the right place to train it.
Pencil marks
When a cell allows more than one value, don't guess — annotate. Pencil marks are the small candidate digits you note in the corner of a cell to track what can still go there. In the game, they're one tap away in pencil mode.
Two habits worth building. First: only mark where it helps — a grid buried under candidates confuses more than it clarifies. Second: keep them current. Every placed digit removes candidates along its row, column and box (that happens automatically here, but you won't always play here). From the medium level up, pencil marks stop being notes and become the surface the techniques actually work on.
The most common mistakes
The first is guessing: a digit that goes in "by eye" rather than by deduction will sooner or later contradict the grid — and tracing back to where it all went wrong is the worst part of the game. The second is forgetting one of the three constraints, typically the box, when your attention is locked on rows and columns. The third is careless candidates: a wrong pencil mark weighs as much as a wrong digit, because later deductions lean on it.
Patience isn't a style choice. It's the method.
Beyond the rules: techniques
The rules take five minutes; the real game starts afterwards, with deduction techniques — recurring ways of reading the grid that let you place digits or eliminate candidates. Difficulty levels here are defined exactly that way: by the techniques a puzzle demands. You'll find them explained step by step in the technique guides, and the home page is always one tap away to put it all into practice.