sudokly
Evil · Typical solve: 45 to 90 minutes or more

Evil Sudoku, Free Online

Maximum difficulty. Forcing chains and beyond.

EasyMediumHardExpertEvil
Evil00:00✕ 0
About evil

What evil sudoku feels like.

Evil sudoku sits at 22 to 24 clues, close to the practical lower bound for logical solvability. You will cycle through XY-wing, swordfish, coloring and forcing chains. A single sitting can take an hour.

Typical solve time
45 to 90 minutes or more
Who it's for
Sudoku obsessives. People who finish expert puzzles bored.
Techniques
Forcing chains, Coloring (multi-color), XYZ-wing, BUG, Unique rectangles

Evil sudoku FAQ

Is evil sudoku solvable without guessing?

Yes, but it requires the full toolbox: XY-wing, swordfish, coloring, forcing chains and unique rectangles. Every Sudokly evil sudoku is verified logically solvable. If you are tempted to guess, take a break and come back.

How long does evil sudoku take?

Plan for 45 to 90 minutes. Some evil puzzles take longer. Many players solve evil over multiple sittings. That is what the auto-save is for.

What is the minimum clue count for evil sudoku?

Sudokly evil sudoku puzzles have 22 to 24 clues. The mathematical minimum for a uniquely solvable sudoku is 17, but those require techniques that are not fun for humans.

Should I learn evil techniques before tackling evil?

Yes. Read our strategy pages on forcing chains and coloring first, otherwise you will burn out fast. Evil sudoku is satisfying when you have the tools, miserable when you do not.

Are evil puzzles unique?

Yes, every one. We brute-force verify uniqueness during generation. A puzzle with multiple solutions never gets published.