The Rules of Sudoku Explained for Complete Beginners

The board

A Sudoku board is a large square split into 81 cells, arranged as 9 rows and 9 columns. Those 81 cells are also grouped into nine smaller squares of 3 by 3, usually called boxes or regions. Rows, columns and boxes are the three shapes you care about, and every rule is built on them.

When a puzzle begins, some cells are already filled. These are your starting clues, and they never change. In Shapedoku we call them locked shapes or ancient marks. The rest of the cells are empty, and filling them in correctly is the whole game.

The one rule that matters

There is really only one rule, stated three ways. Each row must contain every value exactly once. Each column must contain every value exactly once. Each 3 by 3 box must contain every value exactly once. In classic Sudoku the values are the numbers 1 to 9. In Shapedoku they are nine shapes, but the logic is identical.

Put simply, no value may repeat inside the same row, column or box. If you ever see the same value twice in any of those three groups, something is wrong.

What winning looks like

You win when every cell is filled and all three rules hold across the entire board at once. A finished Sudoku has each value appearing nine times in total, once in every row, once in every column and once in every box. A good puzzle has exactly one correct solution, so there is always a path to the answer through logic alone.

A quick example

Imagine a row that already holds eight different shapes and has one empty cell. Only one shape is missing from that row, so it must go in the empty cell. That is Sudoku in miniature. You look at what a group already contains, work out what it still needs, and place the value that is forced.

Common misunderstandings

• Diagonals do not matter in classic Sudoku. Only rows, columns and boxes have the rule.
• You never need math. Sudoku is about placement and logic, not addition.
• There is no guessing in a well made puzzle. Every step can be reasoned out.
• The starting clues are fixed. You only fill the empty cells.

That is the entire rule set. If you understand rows, columns and boxes, you already know how to play. The best way to lock it in is to try one. Open an Easy board in Shapedoku and place a few shapes. The rules will feel natural within a minute.