BACK TO THE GAME

Use the list below to navigate specific topics about Sudoku.

### How to play

Difficulty level. Our free online version of web Sudoku follows in the number puzzle's classic tradition; no pen or pencil is needed! As you start the puzzle, you can choose your sudoku difficulty.

We offer Sudoku for beginners, medium Sudoku, and Sudoku for experts:

Scanning method. The most basic technique for solving Sudoku puzzles is to use the scanning method. This involves picking a number and then looking at rows and columns across the grid containing that number. The goal is to look at all the boxes where the number can’t be placed, hopefully leaving the one box where it should be.

Scanning is especially effective when you’re looking at both rows and columns at the same time. In grids with many unfilled squares, this is often the only way to narrow down where to place a number.

This process of elimination is a fast, easy, and highly effective method to solve lower-level puzzles. Even when solving a hard puzzle, it’s a great opening move to fill in a good number of squares.

You can access the menu by clicking the icon on the top right of the screen.

In the menu, you'll have several different options to play as you like.

Use slash notes. When using notes, this option will automatically slash any numbers that you've already inserted in that specific line or space, in order to help you keep track of how many you have to go.

Auto cleanup. This option eliminates your pencil notes when necessary, without you having to manually do so.

CleanupLike the eraser option in the game, this option allows you to erase any notes or numbers that you've set.

Place notes. This option allows you to place notes in your board instead of the final number.

Show timer. This allows you to choose whether you'd like to see the timer or not. Please know that the timer will affect your final score regardless of whether you see it.

Show errors. This allows you to see which numbers you've placed are wrong by coloring them red.

RevealThis lets you reveal a single cell of the puzzle, or the entire puzzle that hasn't been solved yet. The percentage that is revealed with this option will not count towards your final score.

RevealUse this option to print your Sudoku puzzle so you can play it in real paper.

SaveYou can save your current progress with this option, so that you can return to it later.

HelpIf you're in need, you can use this option to check a careful explanation of the game, as well of all of the menu options available.

ResetThis option erases every number and note you've typed and allows you to start over from the beginning with a new timer.

Exit. This will exit the game, and refresh your webpage.

You also have three icons on the left which allow you to use options without having to click on the menu. The Arrow allows you to undo your last move. The Pencil allows you to take notes, and the Eraser allows you to erase any of your inserted numbers or notes.

### Tips

Scanning method. The most basic technique for solving Sudoku puzzles is to use the scanning method. This involves picking a number and then looking at rows and columns across the grid containing that number. The goal is to look at all the boxes where the number can’t be placed, hopefully leaving the one box where it should be.

Scanning is especially effective when you’re looking at both rows and columns at the same time. In grids with many unfilled squares, this is often the only way to narrow down where to place a number.

This process of elimination is a fast, easy, and highly effective method to solve lower-level puzzles. Even when solving a hard puzzle, it’s a great opening move to fill in a good number of squares.

Pencil notes. However, there will come the point when the scanning method mentioned above won’t cut it. Here is where using the pencil marking comes in. The idea is to use pencil notes to fill a space with all possible number combinations. You’ll then analyze the whole board to figure out which number combinations work.

Disjointed pair. One common problem you’ll encounter is a disjointed pair. This is when two numbers can only be placed in two squares, but you don’t know which number goes into which space. When such pairs are apparent, it’s called a naked pair. Otherwise, it’s referred to as a hidden pair.

While you can’t solve disjointed pairs directly on their own, you can use them to deduce where other numbers should be.

`EXAMPLE: if you have three spaces left on a grid, and two of those is disjointed pair, then you know the third can only be placed on the remaining space`

X-wing. A very advanced approach for solving truly challenging puzzles is the X-Wing technique. This happens when the spaces you’re trying to solve form an X shape or are in the corners of an imaginary square. This gives you a new logic constraint that allows you to eliminate spaces further. While useful, the X pattern required for this technique is pretty rare in practice.

### Scoring

General Formula:

Final Score = Puzzle Score  * (Difficulty Bonus +  Time Bonus)

The Puzzle Score. It equals the % of the puzzle that was completed without help.

Difficulty Bonus:

Easy: 100 points

Medium: 200 points

Hard: 300 points

Expert: 400 points

Time Bonus:

Easy: 180 (3 min) minus the time spent

Medium: 360 (6 min) minus the time spent

Hard: 540 (9 min) minus the time spent

Expert: 720 (12 min) minus the time spent

`NOTE: if more time is spent than allowed for the difficulty level, the Time Bonus will be zero`