How are the difficulty levels different?

Easy puzzles have more given digits and can be solved with basic techniques. Medium introduces hidden singles. Hard and Expert require advanced strategies like naked pairs and pointing pairs, with Expert having the fewest starting digits.

Yes. The undo button reverses your last action, and you can undo multiple times back to the starting state.

What do the hints do?

Using a hint fills one empty cell with its correct digit. The game's solver determines which digit belongs there based on the current board state.

Is there a daily Sudoku challenge?

Yes. A new daily challenge is available each day. All players receive the same puzzle, and your solve time appears on the daily leaderboard.

How is the score calculated?

You earn 10 points for each correctly filled cell (excluding the given digits). Faster completion times result in a higher effective score on daily leaderboards.

Play Sudoku Online — Free Classic Number Puzzle

How to Play Sudoku

Objective

Fill every empty cell in the 9x9 grid so that each row, each column, and each 3x3 box contains the digits 1 through 9 exactly once.

Controls

Tap or click an empty cell to select it, then choose a number from the number pad. Use pencil mode to add candidate notes when you are not yet certain of a cell's value.

Step by Step

1Look at the pre-filled (given) numbers on the board.
2Select an empty cell and enter a digit that does not conflict with any number already in the same row, column, or 3x3 box.
3Use pencil marks to track possible candidates for tricky cells.
4If you get stuck, use a hint to reveal the correct digit for one cell.
5Continue until every cell is filled correctly.

Winning

The puzzle is solved when all 81 cells are filled with valid digits and no conflicts remain.

Sudoku Rules

Each row must contain the digits 1 through 9 with no repeats.
Each column must contain the digits 1 through 9 with no repeats.
Each of the nine 3x3 boxes must contain the digits 1 through 9 with no repeats.
Pre-filled cells cannot be changed.
There is exactly one valid solution for every puzzle.

Tips & Strategies

1.Start with rows, columns, or boxes that already have the most digits filled in — fewer candidates means easier deductions.

2.Use pencil marks consistently. Write down every possible candidate for a cell and eliminate them as you place digits elsewhere.

3.Look for naked singles — cells where only one digit is possible — and hidden singles — digits that can only go in one cell within a row, column, or box.

4.When two cells in a box share the same two candidates and no others, those digits can be removed from all other cells in that box (naked pair technique).

5.On harder puzzles, scanning for pointing pairs and box-line reduction will unlock cells that pure singles cannot.

About Sudoku

This version of Sudoku offers four difficulty levels — Easy, Medium, Hard, and Expert — each generated to guarantee a unique solution. The game includes pencil marks for candidate tracking, an undo system so you can backtrack freely, and hints powered by a full constraint solver. Daily challenges provide a fresh puzzle each day with a shared leaderboard so you can compare your solve time against other players. Your progress, score, and best times are tracked automatically.

Frequently Asked Questions

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