Sudoku
Sudoku is the classic logic puzzle: fill a 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. Every board here is generated fresh in your browser and checked to have a single logical solution. Pick Easy, Medium or Hard and start playing — free, no download, no sign-up, and it works entirely offline.
How to play
Sudoku is played on a 9×9 board split into nine 3×3 boxes. Your goal is to fill every empty square with a digit from 1 to 9 so that no digit repeats in any row, any column, or any 3×3 box. The puzzle starts with some numbers already filled in; these are the clues, and they are locked in place. Each board is generated to have exactly one solution, so there is always a single correct answer.
Tap or click a cell to select it, then use the number pad below the grid to enter a digit, or press the 1–9 keys on your keyboard. Move the selection around the board with the arrow keys, and press Backspace, Delete or 0 — or the Erase button — to clear a square you have filled. The cell you select, together with its row, its column, its box and every other cell holding the same digit, is highlighted so you can see related squares at a glance.
If you get stuck, Hint reveals the correct digit for the selected cell, and Check outlines any digits you have placed that clash with another number in the same row, column or box. The timer and the mistake counter in the toolbar keep score as you play, and a new puzzle of any difficulty is one tap away with New Game.
Tips and strategy
Start with the easiest wins. Scan each row, column and box for a digit that already appears eight times — the missing number then has only one square left to go in. From there, look for "hidden singles": a digit that can legally fit in just one square of a row, column or box, even though other numbers might seem to have several homes. Working box by box is often faster than sweeping whole rows, because a single box gives you three directions to check at once.
When scanning stalls, switch to pencil marks. Lightly note every candidate for each empty cell, then hunt for a number that is possible in only one cell of a unit — that is a naked single you can commit with confidence. Cross-hatching, where you trace where a digit can go in neighbouring boxes, resolves most easy and medium boards without any guessing. On harder puzzles, stay disciplined: place only digits you can justify from the numbers already on the board, and use Undo freely rather than committing to a guess you may have to unpick later.