CLASSIC RULES
Sudoku Rules
Fill all 81 cells so that each row, each column and each outlined 3×3 box contains the digits 1 to 9 exactly once.
Rows, columns and boxes
Each horizontal row, vertical column and thick-bordered 3×3 box must contain every digit from 1 to 9 once. A digit may not repeat inside any of those three units.
Givens cannot change
The starting digits define the puzzle and remain fixed. Every value you add must agree with all givens in its row, column and box.
No arithmetic required
Digits are symbols in classic Sudoku. You do not add, subtract or calculate them; you eliminate positions by logic.
Candidates are temporary notes
Small candidate marks record values that are still possible. They are not final entries and should be removed whenever a placement rules them out.
One logical solution
Sudoku Genius validates its included catalogue so each puzzle has one intended solution. A correct solve fills the entire grid without guessing or contradiction.
When a move is valid
Before placing a digit, confirm that the same digit is absent from the cell’s row, column and box and that your deduction leaves the puzzle consistent.