Play Killer Sudoku — Free
The Sudoku variant with sum cages. Fill every row, column and 3×3 box with 1–9 — no repeats — while the digits inside each dashed cage add up to the small target in its corner and never repeat. Hand-crafted Easy, Medium and Hard boards, each with one guaranteed solution.
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What is Killer Sudoku?
Killer Sudoku is the arithmetic cousin of classic Sudoku — a 9×9 logic puzzle that keeps everything you already love about the original and adds a clever layer of addition on top. Just like ordinary Sudoku, your goal is to fill the grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. What makes it "killer" is that the grid is also carved into dashed outlines called cages, and each cage carries a small target number in its corner. The digits you place inside a cage must add up to that target, and — crucially — no digit may repeat within a single cage. The two rule sets feed each other: the Sudoku constraints tell you which digits are legal in a cell, and the cage sums tell you how those digits have to combine.
The twist that gives Killer Sudoku its bite is that it usually begins with very few given numbers — often none at all. Where a normal Sudoku hands you a scattering of clues to build from, a Killer Sudoku expects the cages to do that job. A cage marked "4" spanning two cells, for instance, can only ever be a 1 and a 3, and that single deduction can unlock a whole region of the board. Because of this, Killer Sudoku rewards a slightly different kind of thinking — you are constantly weighing which sets of distinct digits can hit a target while still obeying the no-repeats rule of every row, column and box. Every puzzle on vygam is hand-crafted with a single guaranteed solution reachable by pure logic, so you never have to guess: there is always a next forced move waiting to be spotted, and a full 9×9 board makes for a deeply satisfying sit-down solve.
How to Play Killer Sudoku
A cage is simply a group of cells joined by a dashed border with one number printed in its corner. That number is the exact total the cage's digits must reach when you add them together — a three-cell cage marked "8" might be 1 + 3 + 4, but never 2 + 3 + 3, because a digit can never repeat inside a cage. There is one wonderfully useful shortcut hiding in the rules, often called the rule of 45: because every row, column and 3×3 box contains 1 through 9 exactly once, the digits in any of those "houses" always add up to 45. If the cages sitting inside a house account for every cell but one, subtract their combined total from 45 and you have found the odd cell out.
A placement or a finished grid is wrong whenever it breaks one of these rules:
- a digit from 1 to 9 appears more than once in the same row;
- a digit from 1 to 9 appears more than once in the same column, or in the same 3×3 box;
- a digit repeats inside a single cage, even if the cage's total would otherwise be correct;
- a completed cage's digits do not add up to its target sum.
Killer Sudoku Tips & Strategy
Killer Sudoku rewards a patient order of attack. The idea is to let the cage sums and the ordinary Sudoku rules reinforce one another — every digit a cage forces removes a candidate from its row, column and box, and every house you nearly complete narrows what its cages can contain. These techniques will get even the Hard boards moving.
Lean on the rule of 45
The single most powerful tool in Killer Sudoku is that every row, column and 3×3 box sums to 45. Find a house where the cages inside it cover all nine cells but one, add those cage targets together, and subtract from 45 — the remainder is the value of that stray cell, handed to you for free. The same trick works when a cage pokes just one or two cells outside a house: total the cages, compare with 45, and the small overshoot or shortfall pins down the outlying digits. Scanning for these near-complete houses is usually the fastest way to plant your first certain numbers on a clueless board.
Memorise the tight cage combinations
Some cage sums leave almost no freedom, and knowing them on sight is a huge edge. A two-cell "3" must be 1 and 2; a two-cell "4" must be 1 and 3; a two-cell "16" must be 7 and 9; a two-cell "17" must be 8 and 9. At the other extreme a three-cell "6" can only be 1-2-3 and a three-cell "24" only 7-8-9. Lock these forced cages in first, because each one plants a definite pair or trio of digits whose eliminations ripple across the whole grid.
List a cage's options, then prune
For a cage with room to breathe, write down every set of distinct digits that could reach its target, then throw out the sets that clash with what its row, column or box already holds. A three-cell "15" could be 1-5-9, 1-6-8, 2-4-9, 2-5-8, 2-6-7, 3-4-8, 3-5-7 or 4-5-6 — but if that cage shares a box that already contains a 9, every option with a 9 disappears at once. Pencil-marking the survivors in each cell turns a fuzzy cage into a short, checkable shortlist you can finish with normal Sudoku scanning.
Hunt for naked pairs and locked sums
When two cells in the same house are both narrowed to the same two candidates — say both can only be 4 or 7 — those two digits are locked into that pair, and you can strike 4 and 7 out of every other cell in the house. Killer cages create these naked pairs constantly: a two-cell "11" that must be a 2 and a 9, or a "13" that must be a 4 and a 9, behaves exactly like a naked pair the moment it sits inside a shared row, column or box. Combining cage combinations with classic pair and triple logic is what carries you through the toughest grids.
Difficulty Levels & Puzzles
vygam ships three tiers of hand-crafted Killer Sudoku, and every puzzle is authored with a single guaranteed solution reachable by logic alone. Easy boards give you a helping of starting digits and lean on small two- and three-cell cages, so you can settle into the rhythm of reading a sum, spotting a forced pair and letting the rule of 45 do the heavy lifting. They are the perfect place to get comfortable with how the cages and the Sudoku grid talk to each other.
Medium puzzles pull back most of the givens and mix in larger cages, so you rely more on listing combinations and cross-referencing houses. Hard puzzles hand you the fewest clues — often none at all — and lean on bigger, sprawling cages, so a single well-read sum can carry more weight than any given digit. Your fastest completion is stored separately for each difficulty in your browser, so you can chase a personal-best time on Easy while slowly working up to the Hard set. Tap New puzzle at any time to move to the next board in the current tier — the collection cycles, so there is always another grid waiting.
Killer Sudoku vs Sudoku & Other Logic Puzzles
If you already enjoy Sudoku, Kakuro, Calcudoku or Futoshiki, Killer Sudoku will feel like a familiar friend wearing a new hat. It shares Sudoku's exact grid and house rules — fill each row, column and 3×3 box with 1 to 9 — but it strips away most of the starting clues and replaces them with cages that add up to fixed totals, so you reason forward from sums rather than from scattered given digits. That makes the opening of a Killer Sudoku a very different experience: instead of hunting for a lone forced cell, you are working out which combinations a cage can possibly hold.
Compared with Kakuro, which also uses addition, Killer Sudoku keeps the full 9×9 Sudoku framework and its no-repeat houses, where Kakuro is a crossword of separate sum runs with no boxes. Against Calcudoku the difference is the operations: Calcudoku's cages can add, subtract, multiply or divide on smaller Latin-square grids, while Killer Sudoku sticks to pure addition on the classic nine-by-nine. And against Futoshiki, which layers greater-than and less-than signs onto a Latin square, Killer Sudoku trades ordering clues for arithmetic ones. What unites all of them is transparent, guess-free deduction — there is always a next logical step — which is exactly why Killer Sudoku has become a favourite for solvers who have mastered the classic and want a fresh, chewier challenge in the browser.
FAQ
Is Killer Sudoku free to play?
Yes — Killer Sudoku on vygam is completely free and plays instantly in your browser. There is no download and no sign-up; you can play Easy, Medium and Hard puzzles on phone, tablet or desktop whenever you like.
How do you play Killer Sudoku?
Fill the 9x9 grid so every row, every column and every 3x3 box contains the digits 1 to 9 exactly once, just like ordinary Sudoku. On top of that, the grid is divided into dashed groups called cages, and the digits inside each cage must add up to the small target sum printed in its corner without any digit repeating inside that cage. When the whole grid obeys the Sudoku rules and every cage adds to its target, the puzzle is solved.
What is the 45 rule in Killer Sudoku?
Because every row, column and 3x3 box holds the digits 1 to 9 exactly once, the numbers in any of those houses always add up to 45. That fixed total is the most useful trick in Killer Sudoku: if the cages inside a house cover all but one cell, you subtract their combined sum from 45 to find the missing cell, and you can extend the same idea to cells that stick out of a house by a square or two.
Do you need to be good at math for Killer Sudoku?
Not really. Killer Sudoku only uses the digits 1 to 9 and simple addition, and every cage total is small enough to add up in your head. There is no multiplication, subtraction or algebra. The real work is logic — deciding which combination of distinct digits can make a cage's sum while still fitting the no-repeat rules of its rows, columns and boxes.
Is Killer Sudoku harder than regular Sudoku?
Killer Sudoku is generally a step tougher because it usually starts with few or no given digits, so the cage sums have to do the work the clues do in a normal Sudoku. In return the cages hand you extra information: each one tells you both a target total and that its digits are all different. Once you are comfortable with cage combinations and the 45 rule, a Killer Sudoku is very rewarding to crack.