Killer Sudoku Online Help


Killer Sudoku follows the same rules as regular Sudoku in that each row, column and block must contain one of the numbers from "1" to "9". No number may appear more than once in any row, column, or block.
It differs in that it introduces "cages" - groups of adjacent 2, 3, 4, or 5 cells demarcated by dotted lines. Each cage indicates the total that it's cell values sum to.
For example, in the puzzle to the right, the cage shaded green has cells totalling 19. Also, the cells in each cage must be unique even if they are not in the same row, column or block.

How To Play

  • Click the "New" button and select a difficulty 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 or by using the mouse wheel. (See tips below.)

Input Tips


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 or use the mouse wheel.
  • Press the "U" key to undo last input.
  • Press the "C" key to change all cells with one possible (pencil mark) to pen.
  • Hold Shift key down to always enter in pencil (not operable with the number pad).

Other Tips

  • Clicking the combo icon will show a dialog allowing you to enter the number of unknown cells and their total to get all the digit combinations that sum to that total.
    If you are not using Active Number Mode (see below), the combinations for the cage containing the highlighted cell will be shown. This is quicker as you do not need to enter the number of cells and total first.
  • 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 "Edit".
  • 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 Edit->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. (If not in Active Number Mode, the mouse wheel will toggle between pen and pencil.)

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

Description Of Menu Options


Main options to do with generating new puzzles.

The first three options will generate a puzzle at three different difficulty levels. There is one new puzzle per level per day.

Note: All puzzles are solvable by pure logic - no guessing required!


Undoes the last input. You can undo right back to the beginning of the puzzle (unless you loaded a partially solved one). There is an Undo button which performs the same task, also the "U" key is a shortcut to this option.
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.
Pencil Marks to Pen
This option will convert all cells that have one pencil mark to a pen mark. The "C" key is a shortcut key for this option.
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.
Loads the last saved puzzle on this computer.
This will print the puzzle at the state it is currently displayed in the grid.
Here you may set various preferences. They are remembered and will reload from what was last set on that computer.

Active Number Mode: This toggle Active Number Mode, described above.

Show Pen/Pencil Cursor: Toggles whether the pen/pencil cursor is displayed over the grid or just the standard finger cursor. (Does not apply if Active Number Mode set.)

Auto Show Errors: If checked, as you enter a number in a cell, it will display in red if incorrect.

Auto Remove Pencil marks: If checked, when you enter a final (pen) number in a cell, that number will be automatically removed from the possibles in all other cells in same row, column or block.

You can also customize the color of the grid, the dotted cage lines and the numbers.

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.
Cage Combinations
This helps you see the possible combinations for cells in a cage.
In the non-Flash version and not using Active Number Mode, select a cell from the cage you which to see combinations and they will be shown in the message area. If using Active Number Mode, you will need to enter the number of cells and total first to see the combinations (as there is no way to identify the cage you are interested in).
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.
If a cell is solvable via basic solving techniques, then the clue 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.

If the only way to solve a cell is via more advanced solving techniques (as found in Hard and Tough puzzles), then the clue will point you to the cell and say what technique(s) is/are required. This is not as helpful and you may need to resort to the "Solve One Cell" if still stuck.

Solve One Cell
This is a very powerful option, especially as a learning tool. It will fill in one of the cells and displays the reason why that number is the answer to the cell.
Possibles Basic
This option will show you the possible numbers for each unsolved cell using the most basic logic technique ie it looks at what numbers are already present in the same block, row and column.
Possibles Cage
This option uses the basic strategies using the cage numbers to further reduce the possibles for each unsolved cell.
Possibles Hard
This option goes further by using more advanced solving strategies in determining possible numbers for each unsolved cell.
Shows the completed solution.