Evil Sudoku

The hardest classic 9×9 puzzles — sparse givens, no easy singles, advanced techniques required. Pure logic, no guessing.

Easy Medium Hard Expert Evil Extreme

Play evil sudoku online — free, unlimited, and built so every deduction follows from logic. You will need X-Wings, Swordfish, and full pencil marks to crack these grids.

6
7
5
8
3
1
8
3
2
1
6
3
2
5
8
2
4
7
5
9
9
5
9
3
7
Mistakes
0/3
Score
-
Time
00:00
Ready for Even Harder? Try Extreme →
Progress0%
Evil · Classic Sudoku Learn the Techniques →

What Makes a Sudoku Evil

An evil sudoku is not just a hard puzzle with fewer givens. What defines the rating is the technique profile: at some point in the solve, singles, pairs, and box-line eliminations all run dry, and the only way forward is an advanced pattern. Every evil puzzle here requires at least one of the heavyweight techniques — an X-Wing, where a candidate locked into two cells across two rows wipes that digit from two entire columns; a Swordfish, the three-row, three-column extension of the same idea; or an XY-chain, where linked two-candidate cells pass implications across the board until a digit somewhere is forced.

In practice this means the solve happens in the pencil marks. Expect to fill complete candidate notes early, work in long quiet stretches where no cell resolves, and then unlock five or six placements at once when the key pattern lands. That rhythm — drought, breakthrough, cascade — is the signature of an evil grid. Crucially, none of it is guesswork: each puzzle has a single solution and an unbroken logical path to it.

Evil vs Expert vs Extreme

Evil sits between expert and extreme on our ladder. An honest comparison:

Level Hardest technique needed Pencil marks Typical solve time
Expert Hidden pairs, occasional X-Wing Helpful 10–25 min
Evil X-Wing, Swordfish, XY-chains Essential 20–45 min
Extreme Long chains, multiple stacked fish Essential, heavily managed 40+ min

The honest advice: if expert puzzles still take you over half an hour, stay there a little longer — evil will only frustrate. If you finish expert grids comfortably but extreme feels like a wall, evil is exactly the bridge you want: it demands the advanced patterns without the brutal chain depth. And when evil starts feeling routine, extreme sudoku is waiting. If any technique in the table is unfamiliar, work through the sudoku rules and techniques guide first — ten minutes of reading saves hours of staring.

Evil Sudoku — Frequently Asked Questions

Is evil the hardest Sudoku level?
Almost. On Sudoku.by, evil sits one step below extreme — the absolute top tier. Evil puzzles demand advanced techniques like X-Wing and Swordfish, while extreme adds even longer chains and sparser starting grids. If you can finish evil puzzles consistently, extreme is your next stop.
How long does an evil Sudoku take to solve?
Most experienced players need 20 to 45 minutes per puzzle. Solvers fluent in fish patterns and chains can finish in 12–15 minutes, while a first attempt can easily take over an hour. Speed comes from recognising patterns quickly, not from writing faster — expect your times to drop sharply after your first ten puzzles.
Can evil Sudoku be solved without guessing?
Yes. Every evil puzzle on this page has exactly one solution and a complete logical path to it. You never need to guess — but you do need advanced eliminations. If you feel forced to guess, there is almost always an X-Wing, Swordfish, or chain you have not spotted yet.
What techniques do I need for evil Sudoku?
Beyond singles and pairs, you should be comfortable with pointing pairs, hidden pairs, X-Wing, Swordfish, and simple XY-chains. Full pencil marks are essentially mandatory — evil puzzles are solved in the candidates, not in the cells.
Is evil Sudoku free to play here?
Yes — every puzzle is free, with no signup, no download, and unlimited new puzzles. Creating an account is optional and only needed if you want your times and scores saved to the leaderboard.

Want to sharpen the fundamentals first? Read the complete techniques guide or warm up on expert sudoku.