Play Killer Sudoku Online
A killer sudoku starts from a completely empty grid. Instead of given digits you get cages with a target sum — and between those sums and the sudoku rules, every digit follows. At Sudoku Sagax there are 800 levels, ad-free and with no sign-up required.
What is a killer sudoku?
A killer sudoku is a 9x9 sudoku that gets by without a single given digit. Instead the grid is divided into cages — small groups of squares with a dashed outline and a small number in the corner. That number is the sum of the digits inside the cage.
All the usual sudoku rules still apply: every row, every column and every 3x3 block contains the digits 1 to 9 exactly once. On top of that comes the cage rule: the digits in a cage add up to its stated sum and never repeat within that cage.
The combination produces a puzzle that feels quite unlike ordinary sudoku. You do not start by reading off given digits; you start by breaking sums apart. That is why killer sudoku has a reputation as the connoisseur's variant — and why an empty grid still has exactly one solution.
The rules, explained simply
Three rules, and that is all:
- Sudoku rules still apply. Every row, every column and every 3x3 block contains the digits 1 to 9 exactly once.
- Cage sums add up. The digits inside a cage add up to exactly the small number in its corner.
- No repeats inside a cage. No digit appears twice in the same cage, not even when the cage stretches across several blocks.
Every digit follows inevitably from those three rules. There is never any guessing, and the only arithmetic is mental addition up to 45.
Techniques to get you in
Killer sudoku comes with tools ordinary sudoku does not have. These four will carry you through nearly any level:
- Learn the forced sums. Some sums allow only one set of digits. A two-square cage of 3 is always 1+2; a 17 is always 8+9. A three-square cage of 6 is 1+2+3, and 24 is 7+8+9. These are free starting points — hunt for them first.
- The rule of 45. Every row, column and block holds 1 to 9 and therefore sums to 45. If the cages inside a block account for 38 and one square sticks out, that square is a 7. This rule cracks more puzzles than any other.
- Work out the overhang. The same trick spans several lines: two rows total 90, three total 135. If exactly one square pokes out of the cage pattern, its digit is the difference.
- Write your candidates down. Once you know the possible digit sets for a cage, pencil them into the squares. The sudoku rules will then trim the possibilities away one by one.
Killer sudoku at Sudoku Sagax
You will find killer from the home screen under "All game types". There are 800 levels of its own, a separate leaderboard and a trophy for your first solved killer puzzle. Every level you finish counts towards your daily streak and the shared points pool.
Each puzzle is generated from its level number and has exactly one solution — the same level looks identical for everyone, so best times are comparable. Because killer asks more of you than a plain sudoku, a solved level carries correspondingly more weight in the scoring.
Notes, error highlighting, hints and undo all work as they do in classic sudoku. Everything runs in the browser, ad-free, with no trackers and locally served fonts.
Frequently asked questions
What is a killer sudoku?
A killer sudoku is a 9x9 sudoku with no given digits. The grid is divided into cages instead, each carrying a target sum. The normal sudoku rules apply, and in addition the digits of a cage must add up to its stated sum without repeating inside that cage.
How do you start a killer sudoku?
With the cages whose sum allows only one set of digits: a two-square cage of 3 is 1+2, a 17 is 8+9. After that the rule of 45 helps: every row, column and block sums to 45, so a single square sticking out can be worked out directly.
What is the rule of 45?
Every row, column and 3x3 block contains the digits 1 to 9 and therefore always sums to 45. If you know the sums of all cages in a block except for one square, that square's digit is the difference from 45. The same works across two rows (90) or three (135).
Is killer sudoku harder than normal sudoku?
Getting started is harder, because there is no given digit to hold on to. Once the first cages are settled it plays much like an ordinary sudoku. Knowing the forced sum combinations and the rule of 45 is what gets you in — you never need to add beyond 45.
Do you ever have to guess in killer sudoku?
No. Every puzzle at Sudoku Sagax has exactly one solution, and every digit follows inevitably from the sudoku rules and the cage sums. If you are stuck, a technique is missing, not luck.