Killer Sudoku

This free killer sudoku tool creates killer sudoku puzzles and lets you play them online, right in your web browser. Nothing needs installing and there is no sign-up. Puzzles are made on your device, and nothing is uploaded or stored on a server.

You can choose a 9x9 grid (the default), a 6x6 or a 4x4, and set the difficulty to easy, medium or hard. Every puzzle has exactly one solution, which the built-in solver checks before the puzzle is shown. If you prefer pen and paper, you can also print killer sudoku puzzles with the answers at the end.

How to use the Killer Sudoku tool

1. Pick a size (9x9, 6x6 or 4x4) and a difficulty (easy, medium or hard), then start a new puzzle with New puzzle.
2. Click or tap a cell. The cage helper under the board lists the sets of different digits that can make that cage’s total.
3. Click a number on the number pad, or type the digit. Backspace erases a digit.
4. Turn on pencil mode with the Pencil button, or press P or Space, to write small candidate notes instead of a digit.
5. Press Check to mark wrong cells in red and see how many cells are left.
6. If you get stuck, press Hint for one correct digit, or Reveal cell for a single cell. Show solution displays the whole answer.
7. Use undo and redo (Ctrl/Cmd+Z and Ctrl/Cmd+Y) to step back through your moves.

Two play options help with checking: “Mark repeated digits in red” and “Remove pencil marks automatically,” which clears a digit’s notes from the cells it can see once you place that digit. Arrow keys move around the board, digits enter numbers, and Backspace erases.

Your progress is saved in the browser on this device, so a reload picks up the same puzzle. To continue on another device, use Copy link. To print, open the Print tab and choose 1, 2 or 4 puzzles per page for 9x9 (up to 6 for smaller sizes), on Letter or A4 paper.

What are the killer sudoku rules?

Killer sudoku uses the usual sudoku rules: each row, each column and each 3x3 box must contain the digits 1 to 9 exactly once. It adds cages on top of those rules. A cage is a group of cells outlined with dots, with a small total in one corner.

The digits in a cage must add up to that total, and no digit can repeat inside the same cage. Because a cage can cover cells from more than one row, column or box, cages link parts of the grid together and give you extra clues.

How do you play killer sudoku?

You fill every empty cell with a digit from 1 to 9 so that the sudoku rules and every cage total are satisfied at the same time. Start with the small cages, because they have very few possible combinations. For example, a cage of 3 in two cells must be 1+2, and a cage of 4 in two cells must be 1+3. A cage of 16 in two cells must be 7+9, and a cage of 17 must be 8+9.

Three-cell and four-cell cages also have strong limits. A cage of 6 in three cells must be 1+2+3, and a cage of 24 in three cells must be 7+8+9. A cage of 10 in four cells must be 1+2+3+4, and a cage of 30 in four cells must be 6+7+8+9. Cages with a total of 10 in three cells have four possible sets (1+2+7, 1+3+6, 1+4+5 and 2+3+5), so you narrow them down using the rest of the grid.

How do you solve killer sudoku?

Use the 45 rule. Each row, column and box contains 1 to 9, which adds up to 45. If the cages inside a box cover every cell except one, that last cell equals 45 minus the cage totals. For example, if the cages in a box cover eight cells and add up to 37, the missing cell must be 8.

Combine that with elimination. Write candidate digits in pencil, remove any digit that breaks a row, column, box or cage rule, and look for cells with only one candidate left. Each placed digit removes candidates from the cells that share its row, column, box or cage, so one correct placement often unlocks several more.

What is a cage in killer sudoku?

A cage is a dotted outline around a group of cells, with a small total printed in the top-left corner. Its digits add up to that total, and none of them can repeat. Cages can cover one to five cells, depending on the difficulty.

On easy puzzles, most cages have two cells, and a few have a single cell. On a 9x9 easy puzzle, there are 36 to 43 cages. On hard puzzles, cages have two to five cells and there are no single-cell cages, with 22 to 26 cages on a 9x9 grid. Select any cell and the cage helper shows which digit sets fit that cage’s total.

Frequently asked questions

Does every killer sudoku have one solution?

Yes. Every puzzle the site makes is checked by the built-in solver before it is shown, and it has exactly one solution. You never have to guess between two possible answers.

Do killer sudoku have given numbers?

Many killer sudoku here start with no given digits: the cages alone are enough to find the answer. When the cages alone would allow two solutions, the generator adds one to three given digits to make the answer unique. In a measured set of 45 puzzles, the number of givens ranged from 0 to 3.

Can I print killer sudoku?

Yes. The Print tab prints 1, 2 or 4 puzzles per page for 9x9 grids, and up to 6 per page for smaller sizes. The answers appear at the end, and the paper can be Letter or A4. The cage outlines and totals print in black.

Is killer sudoku free to play online?

Yes. The tool runs in your web browser, is free to use, and needs no sign-up or installation. Nothing you play is uploaded, because puzzles are made on your device.

Is killer sudoku harder than regular sudoku?

It can be. The cage totals give you extra information, but they also add a new rule to keep track of. Easy killer sudoku, with mostly two-cell cages, is often a good starting point for people who already know regular sudoku.

What does the timer count?

The timer runs while you play. It stops when the browser tab is hidden or when you pause the game.

Related tools

• Printable sudoku for classic 9x9 puzzles you can print and solve with a pencil.
• Samurai sudoku when you want five overlapping grids in one puzzle.
• Jigsaw sudoku when you want irregular regions instead of square boxes.
• Hard sudoku when regular sudoku puzzles feel too easy.
• Daily sudoku when you want a new classic puzzle to play each day.
• Sudoku solver when you want to check a grid or see the answer to a puzzle you are stuck on.
• How to play sudoku when you are new to sudoku and want the basic rules first.