Killer Sudoku FAQ

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.

Yes. playkillersudoku.app is free, with no download, no account, and no paywall. The game runs entirely in your browser on desktop and mobile.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.