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Sudoku techniques, from naked singles to X-Wing
Twelve logical moves solve almost every Sudoku. Here they are in the order you will need them, each with real positions from Ninebloom's puzzles. No guessing required.
Beginner
Naked single
A cell with only one digit left.
Read the guideEasy
Hidden single
A digit with only one place left in a row, column or box.
Read the guideMedium
Naked pair
Two cells share the same two candidates.
Read the guideMedium
Pointing pair
A digit in a box lines up in one row or column.
Read the guideHard
Box/line reduction
Pointing pairs, run in reverse.
Read the guideHard
Naked triple
Three cells share three candidates.
Read the guideExpert
X-Wing
A rectangle of one digit across two lines.
Read the guideFiendish
Swordfish
An X-Wing across three lines.
Read the guideFiendish
XY-Wing
Three two-candidate cells that trap a digit.
Read the guideFiendish
XYZ-Wing
An XY-Wing whose pivot also holds the third digit.
Read the guideFiendish
Simple colouring
Follow one digit through its pairs.
Read the guideFiendish
Unique rectangle
A proper puzzle has only one answer.
Read the guide
How the techniques map to difficulty
Ninebloom rates every puzzle by the hardest technique it needs, not by how many digits are missing. Beginner needs only naked singles. Easy adds hidden singles, Medium adds naked and pointing pairs, Hard adds box/line reduction and naked triples, and Expert adds the X-Wing. Fiendish puzzles need at least one move beyond those, from the Swordfish to the unique rectangle.