Sudoku Online

How to Play Sudoku: the Rules in 30 Seconds

Sudoku is played on a 9×9 grid divided into nine 3×3 boxes. Fill the grid so that every row, every column and every 3×3 box contains the digits 1 through 9 exactly once. Some numbers are given at the start — every puzzle is solvable from those clues alone, without guessing.

• Tap a cell, then tap a number (or type on a keyboard). Wrong entries turn red instantly and cost a mistake.
• Solve without mistakes or hints for ★★★. You get 3 hints per puzzle.
• Practice mode gives unlimited puzzles at your chosen difficulty — easy, medium or hard.

Sudoku Strategies for Beginners

Start with scanning: pick a digit and look across rows and boxes to find where it must go. Then try cross-hatching — a number that already appears twice in a set of three boxes often has only one home left in the third. Next, look for single candidates: cells where only one digit can possibly fit, and hidden singles: a digit with only one possible home in a row, column or box. These three techniques alone solve most easy and medium puzzles — advanced patterns like naked pairs and X-wings only appear in genuinely hard grids.

Daily Sudoku: How the Puzzle Works

Every day at midnight UTC a new daily sudoku is published — the same puzzle for everyone in the world, numbered by day. Difficulty rotates from easy to hard through the week, so Monday's grid warms you up and the weekend bites. Your streak is saved on your device: solve the daily puzzle on consecutive days to keep the flame alive, and share your time with friends to compare.

Sudoku vs Killer Sudoku vs Futoshiki

All three are grid-filling logic puzzles, but the constraints differ. Classic sudoku only asks that rows, columns and boxes hold 1–9. Killer sudoku drops most of the given numbers and instead draws dotted cages whose cells must sum to small printed targets — same placement rules, extra arithmetic. Futoshiki shrinks to smaller grids and replaces boxes with less-than and greater-than signs between cells. If you enjoy one, the other two exercise the same deduction muscles from a different angle — try our killer-sudoku-style cage puzzle and futoshiki right here on HanoiStack.

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