Classic Sudoku.
Classic Sudoku uses a 9×9 grid split into nine 3×3 boxes. You need logic and elimination rather than arithmetic: numbers identify the symbols each group must contain.
Play free now No account · Saved progress · Undo includedHow to play
Fill every empty square with a number from 1 to 9. Each row, column and 3 × 3 box must contain every number exactly once.
- Use the numbers 1–9, with no repeats in any row or column.
- Each outlined 3 × 3 box also needs every number exactly once. Printed starting numbers cannot be changed.
- Select an empty square and use the number pad or your keyboard. Notes let you pencil in possible numbers.
- Every puzzle has exactly one solution. Repeated numbers are marked with an ×. Hint reveals a correct number; Undo restores the previous move, including notes.
A rule in action
Check three groups for every entry
Each row, each column and each outlined box must contain 1–9 exactly once. Printed starting numbers cannot be changed. A number that is absent from its row can still conflict with its column or box, so check all three before placing it.
Start with a single missing number
If a row contains 1, 2, 3, 4, 6, 7, 8 and 9, its final square must be 5. Apply the same idea to columns and boxes. When more than one number could fit, turn Notes on and mark candidates. Revisit those notes after nearby entries narrow the possibilities; notes are manual reminders, not an automatic solver.
Use feedback without confusing it with proof
Repeated numbers are marked with an ×. An entry without an × is not necessarily the correct solution: it may be locally legal but cause a conflict later. Hint reveals a correct number and can be undone. Every generated puzzle has exactly one solution, and each variant saves its own numbers and notes.
Common questions
Does a number without an error mark have to be right?
No. Error marks identify repeated numbers in a row, column or box. A different wrong number can remain unmarked until more of the puzzle is filled.
Can I undo a hint?
Yes. Undo restores the previous numbers and notes, including the state before a revealed hint, within the saved 100-step history.
Controls, saves and offline play
Select a square and choose a number. Notes mark candidates, and Erase clears an entry. Arrow keys move your selection; number keys enter values. N toggles notes, and Backspace or Delete erases.
H gives a hint, Ctrl/⌘ Z undoes a move, and F toggles fullscreen where supported. Each variant saves separately on this device. Switching language keeps the same save. Up to 100 undo steps are retained.
First open the game online. Once the menu says “Available offline”, you can reopen it without a connection while your browser retains its data. Clearing site data also removes saved games.