Evil Sudoku
Play the hardest free Sudoku on the web, right here. This is real evil difficulty — the toughest 9×9 we generate — free, in your browser, with no signup.
What makes evil Sudoku so hard?
Evil is the hardest tier on the ladder — sometimes called extreme or master-level Sudoku. The rules never change: every row, column and 3×3 box still holds the digits 1 to 9 exactly once. What changes is the depth of logic you need. An evil board rarely gives up easy cells; it forces you to chain several advanced techniques together before a single number falls into place.
A common myth is that fewer starting clues means a harder puzzle. It doesn’t. Difficulty comes from the hardest technique a puzzle requires, not its clue count — and that is exactly what our evil generator dials up.
Evil vs expert: how much harder?
Expert puzzles are usually solvable with single-cell logic and the occasional pair. Evil puzzles are a clear step up: they routinely need fish patterns and chains, often more than one, working together. The same solver who clears an expert board in a few minutes can spend far longer on an evil one.
If evil feels too brutal right now, step down to expert Sudoku and build your toolkit there before climbing back up.
Techniques you’ll need
To finish an evil board, expect to reach for advanced patterns. We don’t re-teach strategy here — each one links out to sudoku247wiki.com, where it’s explained step by step:
One honest promise: every evil puzzle we serve has a single, unique solution. There is always one correct answer to find — it just takes patience and the right technique.
More evil challenges
Today’s evil puzzle
A fresh date-seeded board every day — same puzzle for everyone.
17-clue minimal puzzles
Evil boards at the proven minimum number of givens.
Printable evil Sudoku
Take an evil puzzle off-screen — print it and solve on paper.
Ready for impossible?
Step up to impossible Sudoku — or try the world’s hardest.
Want the very top of the ladder? Try the world’s hardest Sudoku. Prefer to take an evil challenge on paper? Our sister print site has printable packs, and sudoku247wiki.com covers every technique in depth.
Evil Sudoku FAQ
What is evil Sudoku?
Evil Sudoku is the hardest 9×9 difficulty tier we generate. The rules are exactly the same as any Sudoku — fill every row, column and 3×3 box with 1–9 — but an evil puzzle is defined by the depth of technique it demands to solve, not by having unusual rules. It is sometimes called extreme, master-level, or by its French name, sudoku diabolique.
Is evil Sudoku harder than expert?
Yes. Expert puzzles can usually be cracked with single-cell logic and pairs, while evil puzzles routinely require deeper tools — X-Wings, fish patterns and chains — and several of them in combination. The same solver will spend materially longer on an evil board than on an expert one. If evil is too brutal, step down to expert and work your way up.
How many clues does an evil Sudoku have?
Clue count does not set the difficulty — a 30-clue puzzle can be far harder than a 25-clue one. What makes a puzzle hard is the most advanced technique you need to crack it, not how many givens it starts with. For the record, 17 is the proven minimum number of clues for any uniquely solvable 9×9 Sudoku (McGuire, Tugemann and Civario, 2014), but that is a property of all Sudoku, not a defining trait of the evil tier.
Can I solve evil Sudoku without guessing?
Every puzzle we serve has a single, unique solution, so there is always one correct answer to find. Evil puzzles reward patient, systematic logic and a full toolkit of advanced techniques. We do not claim every board is guess-free — the honest promise is one unique solution per puzzle, every time.
What techniques do I need for evil Sudoku?
Expect to use advanced patterns: X-Wing, Swordfish, XY-Wing, naked and hidden triples, and forcing chains. We do not re-teach strategy here — each technique links out to sudoku247wiki.com, the network’s strategy reference, where it is explained step by step.
Is evil Sudoku free to play?
Yes. Evil Sudoku is completely free and plays instantly in your browser — no download, no account and no paywall. Open the board above and start solving.
The 17-clue minimum is proven in the literature — see the mathematics of Sudoku.