What is Sudoku?
Sudoku is a number-placement puzzle played on a 9×9 grid. Here's what that means, how the rules work, and how a puzzle gets solved.
The short answer
Sudoku is a logic puzzle played on a 9×9 grid split into nine 3×3 boxes. You fill every empty cell with a digit from 1 to 9 so that each row, each column and each 3×3 box contains every digit exactly once. No digit can repeat within the same row, column or box.
A properly generated puzzle starts with some cells already filled in, called givens, and has exactly one valid solution. That means you never have to guess — every empty cell can be worked out through logic alone.
How does Sudoku work?
Each new digit you place has to satisfy three rules at once: it must be new to its row, new to its column, and new to its 3×3 box. As you fill in more of the grid, the number of places left for each remaining digit shrinks, until eventually only one valid option remains for a given cell. That's the core loop of solving: narrow down candidates, spot the cell or digit with only one option left, and repeat.
Is Sudoku a math puzzle?
Not really. Sudoku doesn't involve arithmetic — the digits 1 to 9 are just nine distinct symbols, and you could swap them for letters or shapes without changing the puzzle. Solving Sudoku is about logical deduction and elimination, not calculation. Killer Sudoku is the one variant where simple addition comes into play, since its cages are defined by target sums.
Where did Sudoku come from?
The modern number-placement puzzle was popularized in Japan under the name Sudoku (a shortening of a longer Japanese phrase meaning "the digits must remain single") in the late 1980s, building on earlier number-placement puzzles, and it became a worldwide phenomenon in newspapers and puzzle books during the 2000s.
The three ways to play on Sudokumee
Classic Sudoku is the original grid-and-box format described above. Diagonal Sudoku adds a rule for both long diagonals. Killer Sudoku replaces most of the starting digits with dashed cages that must add up to a target number. See Sudoku modes for the full rules of each, or read the step-by-step how to play guide to start solving.
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