How to play
Tap an empty cell, then a digit. Each row, each column and each of the nine 3×3 boxes must end up with the digits 1 to 9 exactly once. The digits printed in bold are the givens and cannot be changed. A digit that does not belong turns red and counts as a mistake.
- Notes: switch notes on to pencil small candidates into a cell. When you place a digit, it disappears from the notes of its row, column and box by itself.
- The number pad shows how many of each digit are still missing; a digit fades when all nine are in place.
- On a keyboard: type 1–9, move with the arrow keys, erase with Backspace and toggle notes with N.
The four levels
| Level | Givens | Techniques needed |
|---|---|---|
| Easy | 36–40 | Hidden and naked singles |
| Medium | 30–33 | Hidden and naked singles |
| Hard | 25–29 | At least one: locked candidates, naked or hidden pair |
| Expert | 22–26 | At least one: triple, X-Wing, Y-Wing or Swordfish |
A Hard puzzle cannot be finished with singles alone, and an Expert puzzle cannot be finished without one of the advanced patterns. That is checked for every grid before you see it.
The techniques, in plain words
- Hidden single: in a row, column or box, a digit has only one cell left where it can go.
- Naked single: a cell where eight digits are already ruled out by its row, column and box.
- Locked candidates: inside a box, a digit can only sit on one line – so it cannot be anywhere else on that line.
- Naked pair: two cells of a unit that can only hold the same two digits; those digits leave the rest of the unit.
- X-Wing: a digit that, in two rows, fits only in the same two columns – it can be removed from the rest of those columns.
- Y-Wing: three two-candidate cells that pinch a digit out of every cell both “wings” can see.
Getting unstuck
- Sweep the boxes one digit at a time. Take the 1s, then the 2s, and look for the box where a digit has a single place left.
- Count what a row is missing. When only two or three digits are left, their cells often decide themselves.
- Use notes on Hard and Expert. The advanced patterns only show up once the candidates are written down.
Frequently asked questions
Does every puzzle have only one solution?
Yes. Every grid is checked twice: once by a complete computer search, and once by solving it with logic alone. You never have to guess.
What makes a puzzle Hard or Expert?
Not just the number of givens but the techniques it needs. Easy and Medium can be finished with singles alone. Hard needs at least one step such as locked candidates or a pair. Expert needs advanced patterns – a triple, an X-Wing, a Y-Wing or a Swordfish.
What do the hints do?
They fill in the next cell you could find yourself and tell you why that digit must go there. If the next digit only appears after a harder step, the hint names that technique.
Can I play the same puzzle as a friend?
Yes. Send the six-character puzzle code shown under the grid. Your friend types it in and gets exactly the same grid at the same level.
Does Sudoku work offline?
Yes. After the first visit with internet, new puzzles are generated on your device, with no connection needed. Your puzzle in progress is saved too.