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Sudoku is the world's favorite number puzzle game. Fill the 9x9 grid so that every row, every column, and every 3x3 box contains the digits 1 through 9 exactly once. Some cells come pre-filled as givens — those are your clues and can't be changed. Tap or click an empty cell to select it, then enter a digit with the number pad below the board or with the 1-9 keys on your keyboard. Use the arrow keys to move between cells, and Backspace, Delete, or the erase button to clear a mistake. If you place a digit that repeats in its row, column, or box, the conflicting numbers turn red immediately. Hit Check at any time to see whether your entries so far match the solution.
Strategy tips: start with scanning. Pick a digit that already appears often and trace its rows and columns — the boxes they cross often have only one cell left where that digit fits. Next, work the fullest rows, columns, and boxes: a unit with seven or eight digits placed nearly solves itself. When you're stuck, look for "naked singles" — cells where the surrounding row, column, and box already rule out eight of the nine digits. Easy puzzles here leave about 36 givens and fall to pure scanning; medium puzzles leave around 30 and reward patient elimination. Every puzzle is generated fresh and is always solvable. Want a shared challenge? Play the daily sudoku online on the Daily tab — one medium puzzle per day, identical for every player, with a shareable solve time so you can compare with friends.