Beginner guide
How to Play Sudoku
Sudoku is a 9×9 grid divided into nine 3×3 boxes. Some cells start with numbers — your job is to fill in the rest so that every row, every column, and every 3×3 box contains the digits 1 through 9, each exactly once.
The one rule
Each digit 1–9 must appear exactly once in every row, every column, and every 3×3 box. That's it.
Where to start
Look for rows, columns, or boxes that already have many digits filled in. If a row has eight digits, the ninth is decided. If a column has only one missing digit between two given clues, that digit goes in the gap.
Pencil marks
When you can't immediately see the answer, write small candidates in the corner of each cell — every digit that could still go there based on what's not already in that row/column/box. As you fill in more cells, you eliminate candidates, and the puzzle solves itself.
Hidden singles
If a digit can only fit in one cell within a row, column, or box — that's where it goes, even if other digits could also fit that cell. Hidden singles are the most common move beyond simple counting.
Naked pairs
When two cells in a row, column, or box have only the same two candidates (e.g. both can only be 3 or 7), those two digits are locked into those two cells. You can remove 3 and 7 as candidates from every other cell in the same row/column/box.
Ready to try? Pick a difficulty on the home page, or jump into Killer Sudoku — same grid, with cages.