🔢 Sudoku

How to play Sudoku

1. Pick a level. Tap an empty square, then tap a number (or type 1 to 9).
2. Every row, column and 3 by 3 box must hold the numbers 1 to 9 once.
3. Use Notes for pencil marks and Hint if you get stuck.

The rules in detail

Every puzzle is made fresh in your browser from a complete, valid grid, and numbers are only removed while the puzzle still has exactly one solution. Easy keeps 40 starting numbers, Medium 32 and Hard about 27 (a few hard puzzles keep one or two more so the solution stays unique). A wrong number turns red and counts as a mistake; Notes add small pencil marks that are cleared automatically when you place that number nearby. Hint fills the selected square correctly. The timer starts with your first entry, and each level keeps its best time on this device.

Tips

• Start with rows, columns or boxes that are almost full.
• Look for a number that can only go in one square of a box: that is a "hidden single".
• Use Notes on hard puzzles: when two squares in a row can only be the same two numbers, remove those numbers from the rest of the row.

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