Sudoku Rules
Clear Sudoku rules explained simply, including rows, columns, boxes, valid moves, and what counts as a mistake.
Step-by-step: Sudoku Rules
Use this as a clean learning path when you want a practical sequence instead of broad theory.
Step 1
Check the row
Before placing a number, make sure that value is not already present anywhere in the selected row.
Step 2
Check the column
Then confirm the same value does not already appear in the selected column.
Step 3
Check the 3x3 box
Finally, verify the value is also unique inside the 3x3 box that contains the cell.
Step 4
Only place a number when all three are clean
A valid move must satisfy row, column, and box at the same time. If any one unit already contains that number, the move is invalid.
Sudoku Rules
The formal Sudoku rules are short, which is one reason the puzzle has such wide appeal. The challenge does not come from memorizing many instructions. It comes from applying a few clear rules consistently as the board gets tighter.
Rule 1: Each row uses 1 to 9 once
No row can contain a duplicate number. When the puzzle is solved, every row must contain the digits 1 through 9 exactly one time each.
This means row scanning is one of the simplest ways to eliminate candidates, especially when only a few cells remain empty.
Rule 2: Each column uses 1 to 9 once
Columns follow the same uniqueness rule as rows. If a column already contains a 7, then any other empty cell in that column cannot be 7.
Strong Sudoku play depends on seeing rows and columns as equally important. Many mistakes happen when players focus on only one of them.
Rule 3: Each 3x3 box uses 1 to 9 once
The nine 3x3 boxes are the third layer of Sudoku logic. A number that looks legal in a row can still be wrong if it duplicates inside the box.
This is why effective Sudoku scanning always checks all three units together rather than relying on a single direction.
What counts as an invalid move
A move is invalid if it duplicates a value in the same row, column, or box. A move can also be logically incorrect even if it creates no immediate duplicate, which is why solution-based checking tools are useful for learning.
Today's SUDOKU separates direct conflicts from broader mistakes so you can understand whether you broke a visible rule or simply placed the wrong final value.
Continue learning on Today's SUDOKU
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