How to play Sudoku
A Sudoku board is a 9 × 9 grid split into nine 3 × 3 boxes. Some squares start with a number. Fill every empty square so that each row, each column and each box holds the numbers 1 to 9 once each.
The rules
- Every row holds 1 to 9, with no number twice.
- Every column holds 1 to 9, with no number twice.
- Every 3 × 3 box holds 1 to 9, with no number twice.
- Every board has exactly one answer, and it can be found by logic alone: you never need to guess.
Playing a board
Tap a square, then a number to place it. Notes turns the number pad into pencil marks, so you can write the numbers a square could still hold and cross them off as the board fills. Erase clears a square and Undo takes back your last move.
The levels
Boards come in five levels, each set by the techniques it can call for:
- Easy: singles only.
- Gentle: singles, and a number locked into one line of a box.
- Tough: pairs and triples of notes.
- Expert: patterns that link two or more rows and columns, such as the X-Wing and Swordfish.
- Master: the hardest patterns: chains of linked squares, and patterns that rely on the board having one answer.
The Daily is one new board each day, the same for every player. Solving it keeps your streak.
The clock
- Blitz: five minutes of easy boards, 200 points for each one you finish.
- Nightfall: 60 seconds of daylight, and every box you finish adds 8 more.
- Star trial: ten positions, each needing one technique you have learned. Name the number in the lit square.
Hints
A hint comes in three steps. The first says where to look and gives away no number. The second lights up the reason on the board: the row, box or pair of squares that forces the move. The third points at the answer. Each hint is worked out from the board in front of you, so it always names a move that is true right now.
Where to start
Most boards open with singles. Look for:
- The last gap: a row, column or box with one empty square takes the one number it is missing.
- Only one number fits: every other number is already in the square's row, column or box.
- Only one place left: a number has one square left in a row, column or box, even if that square could hold others.
When singles run out, write notes in every empty square. Pairs, triples and lines then show up as patterns in the notes: two squares in a row that can only hold the same two numbers take those numbers away from the rest of the row (two squares, two numbers). A number that can only sit in one row inside a box is ruled out of that row in the other boxes (stuck in one line).
Each technique has its own page, with a worked board you can step through: all Sudoku techniques.