Sudoku Online Help

How To Play

Move your cursor over the "New Puzzle" menu item and select a skill level from the dropdown menu.
Fill in blanks with the Pen (select a cell, then click on the number you want to enter).
If you’re not 100% sure of a number, you can make a note of it in the cell using the Pencil. To do this, click the "Pencil" icon to be placed in "Pencil mode".
You may enter as many pencil marks as you like in each cell.
To change back to "Pen" mode, click the "Pen" icon. You can also switch between pen and pencil modes quickly by pressing the "P" key. (See tips below.)

Input Tips

Keyboard

If you prefer to use the keyboard rather than the mouse, you may:

Use the arrow keys to navigate around the grid.
Use the number keys to enter a number in the highlighted cell.
Press the space or Delete key to remove any numbers from the highlighted cell.
Press the "P" key to toggle between Pen and Pencil.
Press the "U" key to undo last input.
Hold Shift key down to always enter in pencil.

Other Tips

Click the Undo icon (yellow arrow) to undo last input. You can undo all the way back to the beginning.
Holding the Shift key when clicking on a number in the input panel will pencil that number in. You may find this more convenient than toggling between the Pen and Pencil icons.
To remove just one pencilled number in a cell, enter that number again.
To remove all pencil numbers in a cell, either click the eraser button or simply "pen" the final choice in.
To remove all pencil marks from all cells, use the menu option under "Tools".
New! There is an alternate mode of number input via the mouse called "Active Number Mode" (see below).

Active Number Mode

If you select this mode (via Tools->Preferences menu option), then the number you click from the Number Pad on the right becomes the "active number". The mouse cursor will change to this number and clicking on any cell will enter it in that cell. This is the reverse of the "cell select" mode, where you highlight a cell and then select the number to input. Those that prefer to solve by focusing on one specific number at a time will find this mode much more convenient.

To change the active number, select a new one from the Number Pad or scroll the mouse wheel down/up to increase/decrease the number.

In the Active Number mode, all pencil functionality remains the same as does the ability to use the keyboard.

Description Of Menu Options

New Puzzle Menu

Main options to do with generating new puzzles. The first four options will generate a fresh puzzle at four different skill levels every minute. The first three levels - Beginner, Intermediate and Advanced - follow the tradition of creating puzzles with a symmetrical layout of starting, or fixed, numbers. The fourth level – Supreme - creates puzzles with as few fixed numbers as possible, sometimes as few as 22. At this level, the emphasis is on generating the most challenging puzzles that can be solved using logic, regardless of layout symmetry.

Beginner

The puzzles generated here are for beginners. Start here if you are new to Sudoku.

Intermediate

The next level up from beginner.

Advanced

Starting to get a lot more challenging!

Supreme

This will generate a tough puzzle. All these puzzles are solvable by pure logic.

Input Manually

This option allows you to manually enter a puzzle that you may have got via a newspaper or elsewhere. Enter all the fixed numbers, then click the Done button. The puzzle will then be validated to see that it is solvable, and if so, you can then solve in the same manner as for generated puzzles. All the solve options will be available to help you.

Input Puzzle #

This option allows you to play a puzzle that has been generated before. Every generated puzzle has a unique number (displayed in top right). This option is useful for challenging friends to solve the same one you did.

Solve Menu

Main options to aid in solving puzzles.

Check My Solution

Checks to see if you have solved the puzzle correctly. Any errors made will be shown in red.

Hint

Suggests which cell may be the next easiest to solve. It will not fill in the value - for that you need to select the "Solve One Cell" option.

Clue

This will suggest you look where a particular number is located in a block, row or column and will highlight that area of the grid. This helps you more than the "Hint" option and is the easiest aid you can ask for, save getting the actual answer.

Solve One Cell

This option will fill in one of the cells and displays the reason why that number is the answer to the cell.

Possibles Level 1

This option will show you the obvious possible numbers for each unsolved cell. It does this by looking at what numbers are already present in the same block, row and column.

Possibles Level 2

This option uses more sophisticated algorithms in determining possible numbers for each unsolved cell. It looks at each possible number in each cell and sees if this number can be placed anywhere else on the same row/column/block. If not, the possibles for that cell are reduced to just this number (ie it is the solution for that cell). It goes a step further and looks for pairs of numbers in a row/column/block, that is, two cells that have the same two numbers only. This means that those cells must contain those numbers (although we don't know which is which), and so it allows us to remove those numbers as Possibles from any other cell in the same row (or column or block).

Solve

Solve the puzzle and shows the completed solution.

Tools Menu

Other useful options.

Load

Loads the last saved puzzle on this computer.

Save

Saves the current state of the puzzle to temporary user data on this computer. This is useful if you wish to come back another time to continue solving it, or if you are guessing which may necessitate you to backtrack later on.

Print

This will print the puzzle at the state it is currenly displayed in the grid.

Clear Possibles

This will clear all possibles displayed in the grid.

Clear All Input

This will clear all input (pen and pencil marks) displayed in the grid.

Preferences

Here you may set whether you want to display the timer, whether you wish automatic display of errors, whether you want sound effects or not or whether you want to enable "Active Number" mode. Auto error display means that as you enter a number in a cell, it will display in red if incorrect.

Preferences are remembered and will reload from what was last set on that computer.