Sudoku techniques, plain and simple
From the first naked single to the forcing chains that crack the monsters.
By The Hardest Sudoku Team · Last updated
TL;DR
A plain-English index of the Sudoku solving techniques, from naked singles to forcing chains, ordered by difficulty. Each entry links to a full explanation of how it works and when it applies.
The techniques, easiest to hardest
A Naked Single is a cell that has only one remaining candidate, so that value must go there.
A Hidden Single is a digit that can legally go in only one cell within a row, column or box, even if that cell has other candidates.
Pointing is when all candidates for a digit inside a box fall on a single row or column, letting you eliminate that digit from the rest of that row or column.
Claiming is the mirror of pointing: when a digit's candidates in a row or column all fall inside one box, you eliminate that digit from the rest of that box.
A Naked Pair is two cells in the same unit that share the same two candidates, letting you remove those two digits from every other cell in the unit.
A Hidden Pair is two digits that can only go in the same two cells of a unit, letting you strip all other candidates from those two cells.
An X-Wing is a rectangle pattern where a digit's candidates in two rows line up in the same two columns, allowing eliminations down those columns (or vice versa).
A Swordfish is the three-line generalization of the X-Wing: a digit confined to the same three columns across three rows, enabling column eliminations.
An XY-Wing is a three-cell pattern (a pivot seeing two pincers) that forces a common digit out of any cell both pincers can see.
A Forcing Chain follows a sequence of 'if this, then that' implications until two starting assumptions converge on the same conclusion, which must therefore be true.
Not sure which technique a difficulty needs? See how the SE grade works.