Sudoku Tutorial
From beginner to expert, master Sudoku step by step
Basic Rules
Sudoku is a 9×9 grid divided into nine 3×3 boxes. Fill in numbers 1-9 so that each row, column, and box contains all digits without repetition.
beginner
Single Candidate
When a cell can only contain one number, that is the answer.
beginner
Hidden Single
A number can only go in one cell within a row/column/box, even if that cell has other candidates.
beginner
Naked Pair
Two cells in the same row/column/box have the same two candidates only, so those numbers must go in those two cells.
intermediate
Pointing Pair
When a number in a box appears only in one row or column, it can eliminate that number from other boxes in the same row/column.
intermediate
X-Wing
When a number appears in only the same two columns (or rows) across two rows (or columns), it can be eliminated from other cells in those columns (or rows).
advanced
Swordfish
When a number appears in only the same three columns (or rows) across three rows (or columns), it can be eliminated from other cells in those columns (or rows).
advanced
XY-Wing
Three cells form a chain relationship. Through the two possibilities of the middle cell, the third candidate can be eliminated from the common affected area.
advanced
Skyscraper
Two rows (or columns) where a number only appears in the same two columns (or rows), and those columns (or rows) also contain that number elsewhere, allowing chain elimination.
advanced