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About Sudoku
Sudoku is a number placement puzzle played on a 9×9 grid that is divided into nine 3×3 boxes. Some squares start filled in. Your job is to complete the rest so that every row, every column and every box contains each digit from 1 to 9 exactly once. No arithmetic is involved: the digits could just as well be letters or colors. What matters is logic. Each digit you place removes possibilities from the squares around it, until the rest of the grid is forced.
This version was written for TapGameHub. A new puzzle is generated in your browser whenever you start a game, so you never run out of puzzles, and each one is checked to make sure it has a single solution. You can play with a keyboard or a touchscreen, keep pencil-mark notes and pick up where you left off later.
How to play
- Select an empty square. Its row, column and box are highlighted, and every copy of the same digit on the board is highlighted too.
- Enter a digit from 1 to 9. The starting clues are fixed and cannot be changed. Entering the same digit again clears the square.
- If the digit already appears in the same row, column or box, it turns red. Fix the conflict before you move on.
- Keep going until all 81 squares are filled in correctly. When the puzzle is solved you see your time and your best time for that difficulty.
The number pad shows how many copies of each digit are still left to place. When all nine copies of a digit are on the board, its button is disabled, which is a quick way to see which digits are finished.
Controls
| Action | Keyboard | Mouse or touch |
|---|---|---|
| Select a square | Arrow keys | Click or tap the square |
| Enter a digit | 1 to 9 | Number pad |
| Switch notes mode on or off | N | Notes button |
| Clear a square | Backspace, Delete or 0 | Erase button |
| Undo the last change | Not available | Undo button |
| Reveal a square | Not available | Hint button, three per puzzle |
Click inside the game before you use the keyboard.
Difficulty levels
- Easy starts with 38 clues. Most squares can be solved by finding the only place where a digit fits.
- Medium starts with 31 clues. You will use notes more often and need to compare several rows and columns at once.
- Hard starts with 26 clues. Expect long stretches where no digit is obvious and your pencil marks do most of the work.
The game remembers the difficulty you chose last and keeps a separate best time for each level.
Strategy tips
- Start with hidden singles. Pick a digit and check each box. If there is only one square in that box where the digit can go, place it. Then do the same for rows and columns.
- Look for naked singles. If a square has only one possible digit left after you check its row, column and box, that digit belongs there.
- Use notes on harder puzzles. Turn on Notes and write down the candidates for difficult squares. When you place a digit, it is removed automatically from the notes in the same row, column and box, so your marks stay up to date.
- Find pairs. When two squares in the same row, column or box can each hold only the same two digits, those two digits are taken. Remove them from the notes in the other squares of that row, column or box.
- Watch the number pad counts. A digit with only one or two copies left is often the easiest one to finish.
- Save hints for when you are stuck. Select the square you are unsure about before you press Hint, and the hint fills that square instead of a random one.
Frequently asked questions
Does every puzzle have only one solution?
Yes. While a puzzle is being built, a solver checks the grid after each clue is removed. If a removal would allow a second solution, the clue goes back, so there is always exactly one correct way to complete the grid.
Will I get the same puzzles again?
No. Each new game starts from a freshly shuffled, fully solved grid and removes clues in a random order, so you get a different puzzle every time you select New puzzle.
Does a red number mean my answer is wrong?
A red number repeats a digit that is already in the same row, column or box, so it cannot be right. A number that is not red can still be wrong for the final solution, so keep checking your logic as you go.
How do hints work?
You get three hints per puzzle. If the square you have selected is empty or incorrect, a hint fills it with the correct digit. Otherwise, the hint reveals a random square that is still empty or wrong.
Is my game saved if I close the page?
Yes. Your puzzle, notes, remaining hints and time are saved in this browser after every move, along with your best time for each difficulty. Switching to a different difficulty starts a new puzzle and replaces the saved one. Clearing your browser's site data removes these saves.
Can I play Sudoku on a phone or tablet?
Yes. Tap a square, then tap a digit on the number pad. Notes, Erase, Undo and Hint are buttons next to the pad. On a narrow screen the pad sits below the board so the grid stays as large as possible.
Game not loading or controls not responding? See help with loading, controls and saves.
