Play Sudoku Online

Welcome to ClearSudoku. Play free, right in your browser, across five difficulty levels from easy to master, each graded by the logic its puzzles demand. No account, no download, no timer pressure. Your game saves itself on every move.

The rules, in thirty seconds

Sudoku hands you a 9x9 grid, split into nine 3x3 boxes, with some digits already placed. Those starting digits are the givens, and they never move. Here is a real easy puzzle from our bank, exactly as it deals:

1

4

7

4

8

3

2

5

9

1

8

2

4

7

3

2

7

8

6

1

9

7

4

3

1

8

5

4

9

2

8

3

9

1

3

5

2

6

You fill the empty cells under one law: every row, every column and every box must contain the digits 1 through 9 exactly once. This is the same puzzle finished. The green digits are the ones you supply, and the shaded row, column and box each hold all nine digits without a repeat, which is true of every row, column and box on a solved board:

2

6

8

5

9

7

1

3

4

7

4

1

8

6

3

9

5

2

5

9

3

4

2

1

6

7

8

8

1

6

2

4

5

7

9

3

3

2

5

7

8

9

4

6

1

9

7

4

3

1

6

8

2

5

4

8

9

6

3

2

5

1

7

6

5

2

1

7

8

3

4

9

1

3

7

9

5

4

2

8

6

That is the entire rulebook. No arithmetic, no tricks with the starting digits. Each of our puzzles has exactly one solution, and you can reach it by reasoning alone.

Everything you need to solve, nothing else

The board comes with the tools serious players expect, and defaults casual players never have to touch.

• Notes. Tap the pencil (or press N) to mark candidates in a cell. Shown in action just below.
• Auto notes. One tap fills every empty cell with its legal candidates. Bookkeeping done, logic remaining.
• Undo without limits. Every action is reversible, including hints and restarts, and history survives closing the tab. Ctrl+Z works exactly as you would hope.
• Mistake checking, your way. Instant solution check by default, rule check or nothing at all if you prefer. All three modes below.
• Hints that teach position. The hint button fills your selected cell, or the cell a logical solver would go to next.
• A timer with manners. It stays out of sight unless you ask for it, starts on your first move, and pauses behind a blur when you switch tabs. Your time lands on the completion card either way.
• Keyboard, sound and dark mode. Full keyboard play on desktop, soft optional sounds, and light, dark or follow-your-system themes.

Notes and highlighting

The pencil button switches you into note mode. It sits in the action row above the number pad, and it fills in when notes are on. Press it, or the N key:

While it is active, the digits you enter become small candidate marks instead of committed answers. Place a real digit later and the board erases the pencil marks it disproves. Highlighting reads your notes too: select any digit and its pencil-mark twins light up across the board.

45

26

47

4

249

4

38

Mistake checking, three ways

Every player has an opinion about being corrected, so the board offers three modes. The default is solution check: a digit that disagrees with the puzzle’s solution turns red the moment you place it, even when nothing visible contradicts it yet.

4

7

2

9

4

6

8

1

Prefer to find out at the end? Rule check only flags a digit that clashes with a visible digit in its row, column or box, the way paper would. Off means exactly that: no flags at all, purist mode. Both alternatives live behind the gear icon. The running mistake count is a separate switch, off until you turn it on, though your total always appears on the completion card.

A taste of the logic

Most solving starts with scanning: take one digit and ask where it can still live in a box. Below, the two placed 3s block two of the bottom-left box’s three rows. In the one row left, two cells are already taken, so the box’s 3 has exactly one home.

3

3

8

5

3

Rows block rows, columns block columns, and the digit lands where nothing blocks it. Scanning alone clears our easiest puzzles, and the how to play guide walks the entire technique ladder from there.

Difficulty you can trust

Every puzzle on this site is generated offline, checked for a unique solution, then solved by software that only uses human techniques. The hardest technique it needed becomes the puzzle’s difficulty. Easy means singles suffice. Master means forcing chains. Nothing in between is guesswork, and no tier is a renamed clue count.

The upshot: when a page says hard, the puzzle is hard for a reason the page itself can teach you. Pick your level below and see.

Pick your difficulty

• Easy sudokuSolvable with scanning and singles. The right place to learn the habits.
• Medium sudokuIntroduces pencil marks, locked candidates and naked pairs.
• Hard sudokuHidden pairs, triples and X-wings. Full pencil marks recommended.
• Expert sudokuXY-wings, swordfish and coloring. Logic all the way, no guessing.
• Master sudokuForcing chains. The hardest puzzles we generate.

Frequently asked questions

Is there only one solution to each sudoku?

Yes. Every puzzle here is generated with a uniqueness check: clues are removed one at a time, and any removal that would allow a second solution gets put back. One grid, one answer, always.

Is this sudoku site really free?

Yes. Every puzzle and every feature is free, with no account, no download and no paywall. Open the page and play.

Will my game save if I close the tab?

Yes. Your board, notes, time and undo history save in your browser on every move, one game per difficulty. Come back to any difficulty page and your puzzle is exactly where you left it.

Can I play on my phone?

Yes. The board scales to your screen, the number pad sits in thumb reach, and every control meets touch-size guidelines. The same site works on desktop with full keyboard play.