Sudoku

How to play Sudoku

Sudoku is the number-placement puzzle with a single rule: each row, each column and each 3×3 box must contain the digits 1 to 9 exactly once. Every puzzle here is generated with exactly one solution.

• Tap a square, then tap a number to place it. Tap the same number again to take it back.
• Every row, column and 3×3 box must hold the digits 1 to 9 with no repeats.
• Turn on Notes to pencil in candidates when you are not sure yet.
• Fill all 81 squares correctly to finish the puzzle.

Tips that actually help

• Start with the digit that already appears most often — it usually has the fewest empty squares left.
• When two candidates can only fit in the same two squares of a box, no other square in that box can take them.
• Highlighted rows, columns and box make it easy to spot what a square is missing — use the number keys for speed.

What is Sudoku?

Sudoku is a placement puzzle built on a 9×9 grid, divided into nine 3×3 boxes. Some squares are pre-filled; the rest you fill yourself. The only rule is also the whole game: every row, every column and every box must contain each of the digits 1 to 9 exactly once.

You never need to guess

A well-made sudoku has exactly one solution — and crucially, it can be reached by logic alone. That is a design decision, not a coincidence: puzzles are generated by filling a grid and then removing digits one at a time, keeping a digit only if the puzzle still has a single solution after it has been taken away. Every puzzle on this site is built that way.

Why notes are the real skill

Beginners try to hold candidates in their head. Better players write them down. Pencil marks turn an invisible search into a visible one: as soon as a candidate disappears from every square in a row, the digit that remains in a square has to go there. Most of the puzzles rated easy and medium fall to that one technique plus patience.

No timer pressure

The clock here is for your own curiosity. Nothing ends if you take an hour, and there is no limit on mistakes — a wrong digit is simply counted and can be corrected whenever you spot it.

Frequently asked questions