The goal

Fill the grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. Some digits are already in place when you start. You find the rest by reasoning: there is only ever one correct answer, and no guessing is needed.

Reading the board

• Bold dark digits came with the puzzle and can’t be changed. Blue digits are yours.
• Tap a cell and its row, column and box are shaded, and other cells holding the same digit light up.
• A digit that clashes with another in its row, column or box turns red. By default the game does not tell you whether a digit is right until you finish, then it tells you how many mistakes you made. You can ask for wrong digits to be marked as you go (see Highlight mistakes below).

Putting numbers in

Cell first (the default): tap an empty cell, then tap a number. Erase clears the cell you picked, and Undo and Redo step backwards and forwards through your moves.

Number first: tap a number to pick it up, then tap cells to place it. It’s quick when you want the same digit in many places. Tap a cell that already holds that digit to take it back out. Erase works the same way: pick it, then tap cells. The pad is outlined while this mode is on. Use the Number first button to switch, and the button then reads Cell first to switch back.

Notes

Notes are small digits that remember what could still go in a cell. Turn them on with the Notes button, then tap numbers to add or remove notes in the selected cell. When you place a digit, that digit is cleared from the notes of every cell in its row, column and box. Auto fills in every possible note for you.

Hints

Stuck? Hint gives a nudge about where to look. Explain shows the full reasoning and highlights the cells, and you can apply it, or just learn from it and place the digit yourself. If something you have entered is wrong, the hint says so first. Each hint used is counted.

Levels

• Easy: mostly obvious moves
• Medium: scan rows, columns and boxes
• Hard: notes and simple eliminations
• Very Hard: pairs, triples and x-wings
• Expert: wings, chains and rectangles

Levels come from the techniques a puzzle needs, not from how many digits are given. The daily puzzle is the same for everyone each day, and solving it on consecutive days builds a streak, shown on your Statistics page.

Also handy

• Pause hides the board and stops the clock: tap the pause icon beside the timer. Tap the board to carry on. The clock also stops by itself when you leave the app or open a menu.
• Restart Puzzle (in the menu) starts the same puzzle again from the beginning.
• Install it. On a phone, use your browser’s “Add to Home Screen” or “Install app”. It then opens like an app and works offline.
• An account is optional. You never need one to play. See About and the privacy policy for what is kept.

Your settings

Open Settings from the menu. These are kept on your device, and none of them is needed to play.

Hints (on by default)

Shows the Hint button. A hint points at the next logical step and, if you ask, explains it. Turn it off for a game with no help at all.

Hint insights (on by default)

Makes hints say why a technique was needed (nothing simpler worked) and marks the cells of the pattern on the board in color. Needs Hints.

Auto notes button (on by default)

Shows the Auto button, which fills every empty cell with all the digits that could still go there. It asks before replacing notes you have written. It is hidden while Corner and center marks is on.

Number-first mode button (on by default)

Shows the button that switches between cell-first and number-first entry (both are explained below). Cell first means you tap a cell, then tap a number. Number first means you tap a number, then tap as many cells as you like to place it. Hide the button if you only ever use one way.

Remaining counts (off by default)

Shows, in the corner of each number button, how many of that digit are still to be placed. A digit with all nine placed is greyed out either way.

Timer (on by default)

Shows the elapsed time above the board and in the message when you finish. The clock still runs, and your statistics still keep your times, when it is hidden.

Highlight mistakes (off by default)

Shows a digit you have entered in red the moment it is wrong. Leaving it off keeps mistakes private until you finish. Notes and the puzzle’s own digits are never marked.

Haptic feedback (on by default)

A short vibration on phones when you enter a digit, pause or finish. It only works in browsers that support it (Android), never on a computer, and never if your device asks for reduced motion.

Corner and center marks (off by default)

Replaces the single set of notes with two kinds. Corner marks are your candidates, and the hints read them. Center marks are anything else you want to remember. The Notes button becomes Corner and Center, and Auto is hidden.

One Handed Play (off by default)

Choose Right or Left for the hand holding your phone. The number pad becomes a 3 by 3 block at that edge of the screen, and the other buttons stack in three rows beside it, each row level with a row of digits. On Right the pad is at the right and the rows read Auto, Erase, Notes; then Hint and the entry-mode switch; then Undo and Redo, all lined up against the pad. On Left it is the mirror image: the pad is at the left and each row runs in the opposite order, except Undo and Redo. Off keeps the standard layout. It is for phones and tablets: on a desktop screen the buttons always sit in a column beside the board, and the setting isn't shown.

Board colors

Opens a picker with a live sample board, and your choice is saved when you close it. The choices are Classic, High contrast, Midnight, Warm paper, Color-blind friendly. Classic follows your device’s light or dark mode, and every scheme is checked so the numbers stay easy to read.

On a keyboard