Each Sudoku level here is set by the toughest technique a puzzle requires rather than by its count of starting digits, so every puzzle on a level asks for the same set of techniques. Every grid has exactly one solution that can be reached by logic alone, the same promise no-guess Minesweeper makes, and when you get stuck the Hint button teaches the next deduction instead of filling the square for you. Classic Sudoku sits alongside seven variants, Killer among them, plus one shared puzzle every day.
Fill every empty square of the 9×9 grid with a digit from 1 to 9 so that each row, each column and each of the nine bold 3×3 boxes contains every digit exactly once. The printed digits, called givens, cannot be changed, and the puzzle is solved when all 81 squares are filled without breaking a rule. Classic Sudoku involves no arithmetic. The digits could just as well be nine colors, and the whole game is working out which of them can still go in each square.
Tap a square, then a number. With Notes on, the number goes in as a small pencil mark, a candidate you are still considering, and tapping it again removes it. Auto notes writes every legal candidate into every empty square and keeps them up to date as you fill the grid. On a keyboard, type 1 to 9, erase with 0, Backspace or Delete, move with the arrow keys, and use N for notes, H for a hint, Z to undo and Y to redo.
Because each entry is checked against the solution as soon as you place it. A wrong digit turns red and counts as an error even when nothing on the board contradicts it yet, and a digit that clashes with its row, column, box or variant marking turns red too. Clear it before you build on it. The result card lists your time, errors and hints opened.
Before a puzzle is filed, a logic solver works through it from start to finish, and the hardest technique that solve used sets its level. Each level adds new techniques on top of everything below it.
| Level | Techniques it adds |
|---|---|
| Easy | Naked single |
| Medium | Hidden single |
| Hard | Pointing, claiming, naked pair |
| Expert | Naked triple, X-Wing |
| Master | Hidden pair, Skyscraper, 2-String Kite, XY-Wing, Swordfish |
| Extreme | Coloring (color wrap and color trap), W-Wing, XY-Chain |
If you are new to Sudoku, start on Easy or Medium, where scanning rows, columns and boxes is enough and pencil marks are optional. From Hard on, the pointing and pair patterns only show up when your notes are complete.
New game lets you choose the rules and the level separately, so any of the eight rule sets can be played at any of the six levels. How to play explains the active rule with small diagrams, each variant has a Try one step button, and Diagonal, Thermo and Jigsaw also come with a three-step starter set.
| Rules | What is added to classic Sudoku | A good first deduction |
|---|---|---|
| Diagonal | Both long diagonals hold 1–9 once | The center square belongs to both diagonals |
| Thermo | Digits rise from the round bulb to the far end | On a four-square thermometer the bulb is 6 or less and the end 4 or more |
| Killer | Dashed cages add up to their corner number, with no repeats | A two-square cage of 4 is 1 and 3; a three-square cage of 24 is 7, 8 and 9 |
| Kropki | A white dot joins digits one apart, a black dot joins a digit and its double | A square on a black dot can never be 5, 7 or 9 |
| Jigsaw | Nine irregular regions replace the 3×3 boxes | Box-based tricks work on the regions too |
| Arrow | The digits along an arrow add up to its circled digit | A 3 in the circle of a two-square arrow along one row means 1 and 2 |
| Anti-knight | Two squares a chess knight's move apart never match | Each digit you place rules itself out of up to eight more squares |
Killer has one more tool that works anywhere. Every row, column and box adds up to 45, and since the cages here cover the whole grid, subtracting the cages that sit entirely inside a box from 45 gives the total of the squares that poke in from outside.
Most of an easy puzzle comes from two ways of looking. A naked single starts from a square. If its row already holds 1, 2, 4 and 7, its column 3, 5 and 9, and its box a 6, the only digit left for it is 8. A hidden single starts from a digit. Look for the 7 in one box, and if every empty square there but one already sees a 7 in its row or column, that square is the 7, even if other candidates still seem to fit. Switch between the two, and after each placement check its row, column and box, because one answer often hands you the next.
Hard puzzles need candidates. Pointing means all the 4s still possible in a box lie in one row, so no other square in that row, outside the box, can be a 4. Claiming is the mirror image, with a row's only 4s inside one box clearing 4 from the rest of that box. A naked pair is two squares in the same unit that are both down to the same two digits, say 3 and 8, which lets you erase 3 and 8 from every other square in that unit.
X-Wing, the first Expert technique, looks at one digit across two lines. If the 6 in row 3 can only go in columns 2 or 7, and the same is true in row 8, the two 6s must sit on opposite corners of that rectangle. Either way columns 2 and 7 are covered, so 6 can be removed from every other square in those two columns.
The first press of Hint points you at a square, or at a row, column or box and the digit to look for. The second names the technique, with a Learn this one link to its lesson. The third shows the evidence, meaning which squares and candidates force the answer, and only then does the button change to Fill or Apply so you can let it make the move. If two equal digits already clash in a row, column or box, the hint points to that conflict first.
Lessons covers 23 techniques, each practiced on a real board. Sixteen of them match the levels, one each for Easy and Medium, three for Hard, two for Expert, five for Master and four for Extreme, so finishing the lessons up to a level means you know everything that level asks for. The other seven (unique rectangle, empty rectangle, jellyfish, quads, hidden triple, finned X-Wing and XYZ-Wing) are optional, since no puzzle here requires them. After a graded lesson, a button such as Use it on a Hard puzzle starts one at that level.
Today's Sudoku is one classic puzzle a day, picked by the date on your device, so everyone gets the same grid on the same day whatever language they use. Its level is fixed for the day, somewhere from Easy to Expert, and hints are switched off. Regular play takes you back to the normal puzzles. Today's and yesterday's puzzles are both open, earlier dates you finished can be revisited from the Daily calendar, and the Streak in your Record book counts consecutive days, including a puzzle you catch up on a day late.