Mini Sudoku

Fill the grid so every row, every column and every box holds each number exactly once. Pick 4x4 for a couple of minutes, 6x6 to stretch it, or a full 9x9. Every puzzle has exactly one answer, so you never have to guess.

Fill every square so that each row, each column and each outlined box holds every number exactly once. On a 4x4 board that is 1 to 4; on a 6x6 it is 1 to 6; on a 9x9 it is 1 to 9.

The numbers that are already there are the clues. They are printed in bold on a shaded square and cannot be changed - everything you type is in purple on a plain square.

Tap a square, then tap a number from the pad to fill it in. Tapping the same number again rubs it out, and so does Erase. On a keyboard, the arrow keys move around the board, the number keys fill a square, Backspace clears one, and N switches pencil marks on and off.

Turn on Pencil marks when you are not sure yet. The numbers you tap go into the corner of the square as small maybes instead of an answer. Turn it back off to write the real one.

Show mistakes underlines any number that repeats in a row, column or box the moment you write it. Turn it off if you would rather find your own mistakes - the puzzle is the same either way.

Every puzzle is made on your device and checked to have exactly one answer, so you never have to guess. If two numbers both look right, one of them isn't - look again.

New puzzle deals a fresh one at the size and difficulty you have chosen. Everyone in the house who picks the same size and difficulty on the same day gets the same first board, so you can race.

Touch: tap anything on the board to use it. Every button and key is at least 44px tall, so it works with a thumb. The squares of a board are as big as the screen allows - on a small phone some of them are smaller than that, which is why the keys and the number pad, not the squares, are what you type with.

Keyboard: Tab moves between the controls and Enter or Space activates the one you are on. That covers the buttons the game screen always has - Pause, Restart and this page's link - as well as anything the board adds.

Pause stops the clock and freezes the board; Restart gives you a fresh one.

Your score is how long you take, in minutes and seconds. Lower is better.

Play as often as you like. Every game is saved on this device, and your best turns up on the scoreboard.