Classic Sudoku on a 9x9 grid with auto-generated unique puzzles, notes, hints, and per-difficulty best times.

Sudoku is a logic puzzle played on a 9x9 grid divided into nine 3x3 boxes. Your goal is to fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3x3 box contains all nine digits exactly once. A few cells are filled in as clues at the start, and the rest of the solution must be deduced from those clues. Every puzzle generated here is guaranteed to have a unique solution, so you never need to guess — pure logic always gets you home.

Click a cell and type a number with the on-screen keypad or your keyboard. When you are unsure, switch to notes mode to pencil in candidate digits. If you get stuck, the hint button reveals the next logical step, and the error indicator flags any conflict in a row, column, or box the moment it appears. Your fastest time for each difficulty is saved automatically so you can watch your skills improve over weeks and months.

Beginners usually start with the naked single — a cell that has only one possible candidate left — and the hidden single, where a digit can only fit in one cell within a row, column, or box. Intermediate solvers add naked pairs and hidden pairs to eliminate candidates from neighbouring cells, and pointing pairs that link a box to a row or column. Advanced techniques such as X-Wing, Swordfish, and XY-Wing build logical chains across the whole grid, letting you crack puzzles that look impossible at first glance.

Beyond entertainment, Sudoku is a workout for working memory, sustained attention, and pattern recognition. Several studies on cognitive aging have found that adults who regularly engage with number or word puzzles score better on reasoning and short-term memory tests, and many players report that a daily Sudoku session helps them relax, focus, and reach a flow state similar to meditation.

FAQ — Q: What changes between difficulty levels? A: The number of starting clues and the techniques required to solve. Easy puzzles only need naked and hidden singles; Hard and Expert puzzles often require pairs, pointing sets, or X-Wing logic. Q: What are typical solving times? A: Easy 5–10 minutes, Medium 10–20, Hard 20–40, and Expert can take an hour or more. Q: Do hints invalidate my record? A: Hint usage is tracked alongside the time so you can compare runs with and without assistance fairly.