Sudoshi

The Rules of Sudoku

There is really just one rule in Sudoku, applied three ways. Once it clicks, you can play any puzzle in the world.

The one rule

Fill the grid so that each of these never contains the same digit twice:

  • Every row (the nine cells going across) contains 1–9.
  • Every column (the nine cells going down) contains 1–9.
  • Every 3×3 box contains 1–9.

All three conditions must hold at the same time. That single constraint — no repeats in any row, column or box — is the entire rulebook.

5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
The highlighted row must end up containing every digit from 1 to 9.
5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
So must each 3×3 box — here the top-left one.

How to play, step by step

  • Pick an empty cell.
  • Check its row, column and box to see which digits already appear there.
  • If only one digit is left that isn’t already used, it must go in that cell.
  • Fill it in, then repeat — each answer unlocks the next.

You win when every cell is filled and all three conditions hold. Because a valid puzzle has exactly one solution, you never need to guess — if you get stuck, there is always another cell somewhere that only one digit fits.

Difficulty

Puzzles differ only in how many cells are given and how much logic it takes to find each answer. Easy puzzles hand you many clues and simple deductions; harder ones give fewer clues and require you to combine several observations. The rules never change — only the depth of the reasoning.

Ready to try it yourself?

Play now

Keep reading

What is Sudoku?

All guides