➡️ How to play Little Killer Sudoku

By Miguel Arechaga

Little Killer Sudoku is a sum-based variant, a close cousin of Killer Sudoku but much lighter to draw: instead of cages, it uses arrows outside the board. Each arrow indicates the sum of all the cells along the diagonal it points down. It's a very popular variant in competitions and on channels like Cracking the Cryptic. Here are the rules and a few tips.

What is Little Killer Sudoku?

It's a standard 9x9 sudoku where, along the edges of the board, arrows with a number appear. That number is the sum of all the cells in the diagonal the arrow points into. Unlike rows or boxes, numbers can repeat within that diagonal: the arrow only enforces the sum, not uniqueness.

Rules and how to play step by step

1. The sudoku rules apply: 1 to 9 without repeats in each row, column and 3x3 box.
2. Each outer arrow indicates the exact sum of the cells in its diagonal, in the direction it points.
3. Repeats are allowed within a diagonal; the diagonal isn't a sudoku region.
4. You start with some clue cells and fill in the rest with logic. Every puzzle has a unique solution.

Tips to solve Little Killer Sudoku

• Start with short diagonals: an arrow over 2 cells with a very low or very high sum has extremely few combinations (for example, a sum of 4 over two cells can only be 1+3).
• Use the bounds: an N-cell diagonal sums to at least N (all ones) and at most 9N; that rules out a lot of options.
• Combine the sum with the box and column rules that cross the diagonal to pin down values.
• Lean on the classic elimination techniques of sudoku between sums.

How it differs from regular sudoku

Compared to classic sudoku, Little Killer adds arithmetic on the diagonals, but in a lighter way than Killer Sudoku (which uses cages across the whole board). If you enjoy variants with sums and marks, you'll also enjoy Arrow Sudoku.