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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 anytime to flag rule conflicts only — it won't spoil whether a digit matches the hidden 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.