If you have a question that isn't answered here, please get in touch!

Doing puzzles online

To do a puzzle online, tap or click it, or press its Try It Now! button.

Once you're on the online puzzle screen, tap or click the puzzle to highlight one or more cells, then use the keyboard or touchpad to update them. Tap/press a number once to add it, and again to remove it.

You can also add/remove question marks and underlines. Question marks don't have any special meaning, but they're there if you wish to use them. Underlines are described below, along with the other features and controls.

Notes/pencil marks

Notes/pencil marks are small numbers that you can enter into cells when you aren't yet sure of the final answer.

If a cell contains two or more numbers, they will automatically become notes. If you only want one note, first enter the number and then press the note button:

Promote button

Quickly enter a final answer into a cell

If a cell contains many notes/pencil marks and you want to quickly enter a final answer, tap the CLEAR button (or press the C key) then enter the final answer.


The FILL button (or F key) enters all numbers into the highlighted cells. If fill uses cage combinations is enabled (via the Preferences menu), then it only adds numbers that appear in the respective cage combinations, otherwise it adds all numbers from 1 to 9.

For example, consider a 2-cell cage with a sum of 5 - its cage combinations are 1 4 and 2 3. If fill uses cage combinations is enabled, the FILL button will only add the numbers 1 2 3 4 to cells within the cage, as it's impossible for any other numbers to appear there.

Multi-cell selection

Multi-cell selection enables you to highlight multiple cells. There are two ways to do it:

  • Hold down the Shift key and select cells either by clicking them with the mouse or moving with the arrow keys
  • Drag your finger or the mouse (while holding the left mouse button) across the cells

You can update all of the highlighted cells together by using the keyboard or the touchpad as normal.

What is auto-sum?

Auto-sum automatically calculates the sum of multiple cages for you. Highlight the cells in multiple complete cages, and their combined sum will be displayed in the Combinations control.

Cage combinations

When the highlighted cells all belong to the same cage, the Combinations control shows its cage combinations. It updates automatically as you move between cages.

You can tap/click a combination to fade it out, and again to fade it back in, which enables you to keep track of which combinations you have ruled out as you work through a puzzle.


You can use the Calculator to work out the cage combinations for any cage - even one that isn't in the puzzle. Just enter the cage's size (number of cells) and sum.

As with the Combinations control, you can tap/click combinations to fade them in/out.

Hint button

If you get stuck, the Hint button will complete a cell for you. The cell is chosen at random.

Undo button

Use the Undo button to undo up to 500 changes.

If undo includes cage combinations is enabled (via the Preferences menu), then changes to cells (i.e. adding/removing numbers) and cage combinations (i.e. fades in/out) are both undone. Otherwise, only changes to cells are undone.

If cage combinations are included, the Undo button undoes the last cell change and all changes to cage combinations since the previous cell change. In other words, it (a) undoes all changes to cage combinations since the last cell change, (b) undoes the last cell change, and (c) undoes all changes to cage combinations since the previous cell change.

How Am I Doing?

Use the How Am I Doing? button to check your progress and optionally highlight cells that contain mistakes. Also see the question about underlines, below.

Why underline notes/pencil marks?

Underlines control whether notes/pencil marks are checked by the How Am I Doing? button. How Am I Doing? always checks all final/large numbers, but it only checks notes if they're underlined. If the notes are underlined, and the correct answer isn't somewhere in the list, the cell is marked as a mistake.


Your progress for the current puzzle is saved automatically, so you can close your browser or even switch off your computer, then come back later and carry on from where you left off.

Note: If you start a different puzzle, its progress will be saved instead and will overwrite the previous puzzle.

Why can't I see printable puzzles?

Printable puzzles are PDFs, so you need a PDF reader to view/print them. You can download Abode Reader here:

Get adobe reader

Why does a split button appear on the touchpad?

Sometimes a touchpad button will be "split" like this:

Touchpad split 6

This can happen with multi-cell selection. It means that some of the highlighted cells contain the value and some don't. So, for the button above, only some of the highlighted cells contain a 6.

Pressing a split button will add the value to the cells that don't already contain it.

Daily Killer Sudoku