ArchiveHow to playPrintable sudokuAbout Sudoku
About evil puzzles
Evil is our hardest level; some sites call theirs extreme or diabolical. Every evil puzzle starts with only 24–26 digits, and our solver, which always tries the simplest move first, needs a Swordfish or at least three X-Wing / XY-Wing steps to finish it. However hard it gets, there is always a logical next step. No evil puzzle needs a guess.
Press New puzzle for another one at this level. Every puzzle has exactly one solution.
All five levels
| Level | Digits given | What it takes |
|---|---|---|
| Easy | 36–40 | Only naked and hidden singles |
| Medium | 28–34 | At least one pointing pair or box/line reduction; nothing harder |
| Hard | 24–32 | At least one naked or hidden pair or triple; nothing harder |
| Expert | 24–30 | One or two X-Wing or XY-Wing steps |
| Evil | 24–26 | A Swordfish, or three or more X-Wing / XY-Wing steps |
Questions
Is evil sudoku really solvable without guessing?
Yes. Before a puzzle goes into our evil set, a solver works it out using only the techniques on the how-to-play page, one logical step at a time. Puzzles that need trial and error are thrown away.
What is a Swordfish?
The three-row version of an X-Wing: three rows where a digit can only go in the same three columns. Those rows fill the digit's places in all three columns, so the rest of those columns can't have it.
Is this the same as extreme sudoku?
Different sites draw the line in different places, and none of them publish exactly how. What we can say: every evil puzzle here needs the techniques above, and starts with 26 digits or fewer.
Can I stop and finish later?
Yes. Your game saves itself after every move, so you can close the tab and pick it up again on this device.