How Sudoku Works
Fill the 9×9 grid so that every row, every column, and every 3×3 box contains each digit from 1 to 9 exactly once. Pick a difficulty from Easy to Expert, select a cell, and enter digits with the number pad or your keyboard. The stopwatch tracks how fast you solve it.
Wrong entries are highlighted immediately, along with the cells they collide with, and each one adds to your mistake counter. Use notes (pencil marks) to keep track of candidates in a cell. Auto notes fills them in for the whole board once, while Auto candidates keeps them computed live as you play, letting you strike out candidates your own deductions remove. A five-color marking mode lets you paint cells to track coloring chains by hand.
Stuck? A hint reveals the correct digit for the selected cell. You can undo and redo every move, pause the clock at any time (the board hides while paused), and your game is saved locally, so you can safely close the tab and pick up where you left off. And there's a Daily: one shared puzzle per day that ramps from a gentle Monday to a fierce Sunday, with a streak counter and a calendar to catch up on missed days.
Prefer a progression? The Levels campaign climbs ten difficulty tiers of twenty hand-graded puzzles each, from near-full boards to chain-heavy monsters. Every tier ends in a boss, played without hints, and beating it unlocks the next tier, so you can skip ahead whenever the easy levels bore you. Finish all twenty levels of a tier, boss included, and its endless mode opens with a steady supply of puzzles at exactly that difficulty. Each tier also links to the matching Learn techniques, so the campaign doubles as a guided tour through the whole solving toolbox.