Difficulty Labels Explained

Every sudoku puzzle comes with a difficulty label. Easy. Medium. Hard. Expert. Evil. Diabolical. Fiendish. Devilish. The labels vary by source, and almost nobody explains what they mean. The result is a generation of solvers who think a hard puzzle from one newspaper is the same as a hard puzzle from another, and end up confused when one takes ten minutes and the other takes ninety.

Here is what the labels actually correspond to, at least on a well-rated site like Sudokly.

The five tiers

Why the labels disagree across sites

Different sources use different rating algorithms. Some use a scoring system where each technique used contributes points; the total determines the tier. Others manually rate by playtesting, which is more accurate but slower. A few use random clue counts and call it difficulty, which is wrong but common.

Sudokly rates by required technique. An "expert" Sudokly puzzle will reliably ask for at least one X-wing, swordfish or hidden triple. An "evil" Sudokly puzzle will reliably ask for a chain technique. The labels are stable; if you can solve one expert, you can solve any expert from us.

What the clue count tells you (and doesn't)

Clue count is a weak signal. A typical easy has 38 to 45 clues. A typical evil has 22 to 26. But within each tier, clue count varies, and a 24-clue puzzle can be easier than a 30-clue one if the constructor was unlucky with the technique distribution.

The mathematical minimum is 17. Gary McGuire and colleagues proved in 2012 that no valid sudoku has fewer than 17 clues. In practice you will rarely see fewer than 22.

How to pick a difficulty

Pick the tier where the cascade still flows. If you finish in five minutes without thinking, the puzzle is too easy. If you spend twenty minutes scanning and find one placement, the puzzle is too hard. The right tier is the one that feels just slightly out of reach for the technique you currently know.

What "evil" actually means

Evil puzzles are not just harder. They are structurally different. An evil puzzle requires at least one chain technique, which means following hypothetical consequences across several cells before committing to a placement. Some solvers love that mental work. Some hate it. If you are in the second group, expert is the right ceiling.

Not every solver should aim for evil. Many lifelong sudoku readers stay at medium forever and enjoy the puzzle every day. That is fine. The label is not a hierarchy you have to climb.

Browse the tiers at the strategies index, which lists each technique by tier, or jump into the right tier directly: easy, medium, hard, expert, evil.