Common Sudoku Variants

Puzzle shown: Classic Sudoku by Cracking the Cryptic

There are 9 rows, 9 columns, and 9 3×33\times 3 regions. Each square must be filled with a digit from 11 to 99, and digits may not repeat in the same row/column/region.

In almost every sudoku puzzle, these rules will apply.

Image of Sudoku row.

Image of Sudoku column.

Image of Sudoku region.

Local Constraints

Killer Cages

Puzzle shown: Killer Sudoku by Serkan Yürekli

Orthogonally connected cages are drawn. No digits in the same cage may repeat, and if a sum is indicated in the cage, the digits in the cage add up to said sum.

Image of killer cage


Digits must be strictly increasing from the bulb of the thermometer to the end.

Image of thermo


Digits on the arrow must add to the digit in the circle. Digits may repeat if permitted by other Sudoku rules.

Image of arrow

Renban Lines

Renban lines must contain consecutive digits in any order.

Image of renban line

German Whispers

Two directly connected digits on a German whisper must differ by 5 or more.

Image of German whisper


Two digits separated by an X must sum to 10. Two digits separated by a V must sum to 5. (These digits are orthogonally adjacent.)

Image of XV pairs


If two orthogonal digits are separated by a white dot, they must be consecutive. If two orthogonal digits are separated by a black dot, one must be double the other.

Image of Kropki dots

Little Killers

The digits on the diagonal indicated by a Little Killer must add to the sum indicated by the Little Killer. Digits on the diagonal may repeat.

Image of a Little Killer


The first X digits in a row or column in the direction of an X-Sum, where X is the first digit seen in that row or column, must add to the indicated sum.

Image of an X-Sum


Gray circles must contain odd digits, and gray squares must contain even digits.

Image of Odd/Even clues

Between Lines

Digits on a between line must lie between the digits on the endpoints. Digits may repeat on the line.

Image of a Between Line

Global Constraints


A square must contain a digit different from every other square a knight’s move away (2 over and 1 across).

Image of Anti-knight constraint


A square must contain a digit different from every other square a king’s move away (sharing a vertex).

Image of Anti-king constraint