Classic Sudoku

How to play Classic Sudoku

The objective is the familiar 9×9 Sudoku puzzle: every row, column and 3×3 box must contain 1–9 exactly once. Starting clues are fixed. Select an empty cell and enter a number from the on-screen keypad or your keyboard.

The game checks an entry against that puzzle’s verified solution. Three incorrect entries end a standard game. Practice mode keeps the same Sudoku rules and removes the mistake limit.

Easy, Medium, Hard and Expert Sudoku

Choose from 400 puzzles, with 100 at each difficulty. Easy puzzles use singles. Medium adds locked candidates; Hard adds naked pairs. Expert puzzles can require techniques beyond those. The labels describe the recorded solving techniques, rather than just the number of empty cells.

A new game chooses a puzzle from your selected difficulty and avoids the puzzle you are currently playing. Restart puzzle returns to the same starting clues, with a fresh timer and counters. This is a puzzle bank, rather than a daily shared Sudoku challenge.

Pencil notes for Sudoku candidates

Use Notes or press N before entering a digit to toggle a candidate mark in the selected empty cell. Notes are possibilities, not final answers. Switch Notes off when you are ready to place a number.

A correct final number removes that digit’s notes from cells in its row, column and box. Undo restores the previous numbers and notes together, so you can inspect a trial step without rebuilding every candidate by hand.

Hints explain a step before revealing an answer

Hint can identify an incorrect entry to clear, a cell with only one possible number, or the only place for a digit in a row, column or box. Read the explanation and choose whether to apply it.

When these simple techniques do not produce a step, the game offers to reveal one answer from the verified solution. You can decline. Applying a hint increases the hint counter; opening its explanation alone does not.

Undo, mistakes and Practice mode

Undo restores the previous board change, including notes, but it does not refund mistakes or hints. This keeps the standard three-mistake challenge meaningful. Once that limit ends a game, Undo cannot reopen it.

For learning techniques or trying candidates freely, enable Practice before starting. It allows unlimited mistakes while retaining the same objective, notes, hints and verified answers.

Play Sudoku with mouse, touch or keyboard

Select a cell with your mouse or touch, then use the number buttons. On a keyboard, 1–9 enter digits, arrow keys move the selection, N toggles notes, Backspace or Delete erase, and Ctrl/Cmd+Z undo.

The portrait layout keeps the grid and keypad together on smaller screens. A screen-reader board provides the same 81 cells and keyboard commands through labeled grid cells. Pause stops the timer; opening a menu also pauses active solving.

Continue a saved Sudoku puzzle

Your browser can keep the puzzle, numbers, pencil notes, undo history, timer, mistake count and hint count. On return, choose Continue puzzle to resume. Opening New game still lets you cancel and keep the current puzzle.

A conflicting or incompatible save is shown for a decision, rather than silently replaced. Browser saves depend on the same browser storage and game identity. Classic Sudoku retains its existing puzzle bank and save format.

A calm paper puzzle and more logic games

Classic Sudoku keeps the familiar paper garden presentation and legible handwritten digits of the existing game. The grid remains the focus while the rules, notes and difficulty options stay accessible.

Read the Sudoku rules guide if you are learning row, column and box constraints, or browse other logic and number puzzles when you want a different challenge.

When to choose Fish Sudoku

Compare Fish Sudoku with this edition: Classic Sudoku lets you work across a full 9×9 grid in your chosen order. Fish Sudoku leads with an ordered reef route and short blank counts, while also retaining optional full puzzles from its menu.