Sudoku

Fill every row, column, and 3x3 box with numbers 1-9.

About Sudoku

Sudoku is a logic-based number placement puzzle that took the world by storm in the early 2000s. Although its modern form was first published in a Japanese puzzle magazine in 1986 (the name means "single number"), the concept traces back to "Latin Squares" studied by the Swiss mathematician Leonhard Euler in the 18th century. An American puzzle designer named Howard Garns created the modern grid format in 1979, and Japanese publisher Nikoli refined and popularized it.

Sudoku requires no math — only logical deduction. Each puzzle has a unique solution that can be reached through reasoning alone, never guessing. This elegant constraint is what makes Sudoku so satisfying: every placement is provably correct when you find it, and the "aha" moment of cracking a tough cell is deeply rewarding. Puzzles range from gentle warm-ups that take a few minutes to fiendish challenges that test even expert solvers.

This version generates random puzzles at multiple difficulty levels, with immediate feedback on incorrect placements. The clean grid interface highlights your current row, column, and box to help you track constraints visually. Whether you play during a coffee break or settle in for a harder puzzle, it is a perfect exercise for logical thinking.

How to Play

Fill in the empty cells so that every row, column, and 3×3 box contains the digits 1 through 9 exactly once.

Click an empty cell to select it, then click a number (1–9) to place it
Pre-filled cells (given numbers) cannot be changed
Incorrect placements are highlighted in red immediately so you can correct them
Use the eraser or click the same number again to remove a placement
The puzzle is complete when all 81 cells are correctly filled
Each valid puzzle has exactly one solution — no guessing is needed

Tips & Strategy

Scan rows, columns, and boxes for numbers that appear most frequently — they are easiest to place next
Use "naked singles": if a cell can only contain one possible number after eliminating all others, that must be the answer
Look for "hidden singles": when a number can only go in one cell within a row, column, or box
Work through the grid systematically rather than jumping around randomly
On harder puzzles, use pencil marks (mentally note candidates) to track possibilities for each empty cell
If you feel stuck, switch to a different area of the grid — a placement elsewhere often unlocks new deductions