Killer Sudokuplay sudoku with sum cages online, free
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What is Killer Sudoku
Sudoku where the clues are sums
Killer Sudoku — also called sumdoku or sudoku killer — starts with an empty grid. Dotted cages group the cells, and the small number in each cage is the total of its digits, with no digit repeated. Fill every row, column, and 3×3 box with 1–9 while making each cage add up. It blends the logic of sudoku with the arithmetic of kakuro, and every puzzle here can be solved without a single guess.
- Four difficulty levels
- Easy to Expert — difficulty scales the size of the cages, from tidy three-cell cages to sprawling six-cell ones that need the 45 rule and careful elimination.
- One solution, every time
- Each puzzle is generated in your browser and checked by a solver to confirm exactly one valid grid, so you can always solve it by logic without guessing.
- Notes, undo, and hints
- Pencil notes that clear themselves as you place digits, unlimited undo, and a hint that reveals a cell without costing a mistake.
- Progress saved locally
- Best times, win streaks, and your unfinished puzzle are stored on your device — never on a server. Close the tab and pick up where you left off.
How to play
How to play Killer Sudoku
Killer Sudoku is sudoku with arithmetic. Read the cage sums, find the combinations that can only be one way, and let the usual row, column, and box logic do the rest.
- 1
Read the grid
The board is a standard 9×9 sudoku with nine 3×3 boxes. Unlike classic sudoku it starts completely empty. Instead, dotted outlines group the cells into cages, and a small number in the corner of each cage tells you what its digits must add up to.
- 2
Fill rows, columns, and boxes
Every row, every column, and every 3×3 box must contain each digit from 1 to 9 exactly once — the same rule as ordinary sudoku. A digit that repeats in any row, column, or box is wrong.
- 3
Make every cage add up
The digits inside a cage must add up to the cage total, and no digit may appear twice in the same cage. A two-cell cage marked 3 can only be 1 and 2; a three-cell cage marked 24 can only be 7, 8, and 9. These forced combinations are how you break in.
- 4
Solve without guessing
Every puzzle here has exactly one solution and can be solved by logic alone. Use pencil notes to track candidates, lean on the 45 rule for the totals of rows, columns, and boxes, and watch the mistake counter — three wrong digits end the run.
Tips to solve faster
- Start with the cages that have only one possible combination: 3, 4, 16, and 17 in two cells; 6, 7, 23, and 24 in three.
- Every row, column, and box adds up to 45 — use it to find a missing cell when all but one cell of a region is caged.
- Turn on notes and pencil in the digits a cage allows; the row, column, and box then remove the rest.
- A digit cannot repeat inside a cage, so a 3-cell cage totalling 8 can only be 1+2+5 or 1+3+4.
- When a cage spans two rows or columns, compare it with the 45 total to isolate a single leftover cell.
- Single-cell cages are free digits — place them first and let them shrink neighbouring cages.
FAQ
Killer Sudoku, answered
Straight answers about the free Killer Sudoku card game you can play online in your browser.
What is Killer Sudoku?
Killer Sudoku is a sudoku variant that adds arithmetic. You still place 1–9 once in every row, column, and 3×3 box, but the grid starts empty and is divided into dotted cages, each labelled with the sum of its digits. It is also known as sumdoku and sudoku killer.
Is Killer Sudoku free to play here?
Yes. playkillersudoku.app is free, with no download, no account, and no paywall. The game runs entirely in your browser on desktop and mobile.
How is Killer Sudoku different from regular sudoku?
Classic sudoku gives you some starting digits. Killer Sudoku gives you none — instead, cage sums are the clues. That shifts the solving from pattern-scanning to combining arithmetic with the usual row, column, and box logic.
How do I start a puzzle?
Pick Easy, Medium, Hard, or Expert and press Start, or press Play in the header. A brand-new puzzle is generated instantly each time, and New puzzle gives you another at any moment without reloading the page.
Can a digit repeat inside a cage?
No. Every digit in a cage must be different. That is why a two-cell cage of 4 can only be 1 and 3 (not 2 and 2), and why forced combinations exist at all.
What is the 45 rule?
Each row, column, and 3×3 box contains 1 through 9, so its digits add up to 45. When cages fill a region except for one or two cells, adding the cage totals and subtracting from 45 tells you the value of the leftover cells. It is the most important technique on Hard and Expert.
How do mistakes work?
Digits are checked as you place them. A wrong digit turns red and costs one of your three mistakes; after the third the puzzle ends. Correct digits lock in place, and hints never cost a mistake.
What do the difficulty levels change?
Difficulty changes how large the cages can be: up to 3 cells on Easy, 4 on Medium, 5 on Hard, and 6 on Expert. Larger cages have more possible combinations, so they demand more deduction with the 45 rule and elimination.
Does every puzzle have exactly one solution?
Yes. Each puzzle is checked by a solver that confirms there is exactly one valid grid, so you never need to guess — there is always a logical route forward.
Where should I start solving?
Look for single-cell cages (free digits) and cages with only one possible set: 3, 4, 16, 17 in two cells, and 6, 7, 23, 24 in three. Then use pencil notes and the 45 rule. The strategy page walks through each technique.
Are there hints?
Yes. The Hint button fills the selected cell with its correct digit (or the first unsolved cell if none is selected). Hints are unlimited and never count as mistakes, so use them to learn a technique rather than to skip the puzzle.
Can I play Killer Sudoku on my phone?
Yes. The grid and number pad are sized for touch and fit on a phone screen without scrolling. Tap a cell, then tap a number.
Does my progress save?
Yes, on your device. Your best time, games played, and win streak for each difficulty, along with your current unfinished puzzle and your sound setting, are saved in your browser’s local storage. Nothing is uploaded, and clearing site data removes it.
Why did my win streak reset?
A streak counts consecutive wins at one difficulty. It resets when you lose a puzzle by making three mistakes, or when you start a new puzzle after making moves in one you did not finish.