What is Killer Sudoku?
Killer Sudoku keeps every rule of classic 9x9 Sudoku and changes how you get started. Instead of given digits scattered around the grid, the 81 cells are grouped into dashed cages of one to five cells, and each cage shows the sum its digits must add up to. Add one more rule on top: a digit can never repeat inside a cage, even when that cage stretches across more than one row, column or box. Put those together with the ordinary Sudoku rules and, on Medium and Hard, the whole board can be worked out with zero starting digits.
Where to start without any givens
- Extreme sums go first: a 2-cell cage showing 3 is always {1,2}, and one showing 17 is always {8,9}. Small cages with unusually low or high sums narrow down fast.
- The 45 rule does a lot of work: every row, column and 3x3 box sums to 45, so a group of cages sitting neatly inside one of those lets you subtract your way to a leftover cell or pair.
- Notes carry the early game: until a few digits land, you're tracking candidate combinations per cage rather than single digits, so pencil marks matter more here than in classic Sudoku.
Easy reveals 6 given digits, spread across different cages, so newer solvers have a foothold; Medium and Hard start from zero. Every puzzle is generated and then run through a dedicated cage-aware solver that confirms exactly one valid solution, splitting cages and rechecking as needed until that's guaranteed. If you want a longer walkthrough with worked examples, our Killer Sudoku guide covers the rules and a few solving patterns in more depth.
