Sudoku

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.

Tap a cell and enter a digit with the on-screen pad (each key shows how many of that digit are still missing) or with keys 1–9 on your keyboard; arrow keys move the selection and Backspace or Delete clears a cell. Notes mode lets you pencil in candidates, and whenever you place a digit it is cleared from the notes in the same row, column and box for you. A digit that repeats in its row, column or box turns red at once, and there is no mistake limit. Stuck? Up to three hints per game drop the correct digit into the selected cell. Your best time for each difficulty is kept in this browser, and every clear is also posted to that difficulty’s global ranking.

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.