Sudoku

Tips for Sudoku

If you are new to Sudoku, begin on Easy, where around forty digits are already placed and the puzzle only needs the obvious placements. Every puzzle has exactly one solution, so you never need to guess: if you feel stuck, there is always a cell that can be worked out.

Pencil marks are your best tool on Medium and above. Press N to switch to notes and write the possible digits in empty cells, then remove them as the board fills in. They clear themselves when the real digit lands next to them, so keeping them up to date costs little. On Hard and Expert, with only the low twenties given, you will need pointing pairs and locked candidates, which are much easier to spot with notes in place.

When you cannot see the next step, ask for a hint with H. It fills one cell and explains the reason in plain words, which is a good way to learn a new technique. Check, on C, flags any digit that does not match the solution. If you want a tougher test, keep the three-mistakes rule switched on, or turn it off while you learn.

How to play Sudoku

The goal in Sudoku is to fill the nine by nine grid so that every row, every column and every three by three box holds the digits 1 to 9 exactly once. Some digits are already placed when the puzzle starts, and they cannot be changed. Choose a difficulty first: Easy, Medium, Hard or Expert. The harder the level, the fewer digits you start with.

To place a digit, pick an empty cell and enter the number. Look for cells where only one digit can fit, or for a digit that has only one possible place in a row, column or box. When a cell could still hold several digits, write them in as pencil notes and remove them as the grid fills up; notes clear themselves when the real digit lands next to them. Highlighting shows the row, column and box of the cell you are on, and conflicts are marked as they appear. If you choose, the round stops after three mistakes.

The puzzle is solved when every cell is filled correctly, and your time is compared with your best for that level. On a computer you click a cell or move with the arrow keys, then type 1 to 9. On a phone you tap a cell and then a number on the pad. N toggles notes, C checks the board, H gives a hint, P pauses and M mutes.

About Sudoku

Sudoku is a number puzzle with a Japanese name that became a fixture of newspaper puzzle pages around the world. It needs no maths at all, only logic: the digits could just as well be letters or colours, because the only rule is that each one appears once in every row, column and box.

Kiloo's Sudoku builds each puzzle the moment you ask for one and checks that it has exactly one solution, so you never have to guess. Four difficulties take you from Easy, with around forty digits given, to Hard and Expert, where techniques such as pointing pairs and locked candidates come into play. That makes it suit both newcomers and practised solvers. The hint is a good teacher, because it fills one cell and names the reason in plain words, and pencil notes, undo, redo and Check are all there when you want them. The puzzle you are on and your best time for each level are saved in your browser.

Frequently asked questions