Evil is the hardest of our four Sudoku tiers. Each grid arrives with 24 to 27 given digits, and every grid is checked before you see it: the generator only blanks a cell if the puzzle still has exactly one answer. So the solution is always there to be reasoned out. Expect 30 to 60 minutes. Free in your browser, no download and no sign-up.
One thing, mostly: how many digits you start with. Every tier uses the same 9x9 grid and the same three rules. What changes is how much of the grid is already filled in, and therefore how deep the reasoning has to go.
| Tier | Givens | Techniques you need | Typical time |
|---|---|---|---|
| Beginner | 42–46 | Scanning, single candidate | 5–15 min |
| Easy | 36–40 | Scanning, single position | 5–10 min |
| Hard | 28–32 | Naked pairs, hidden pairs | 15–30 min |
| Evil | 24–27 | Pointing pairs, box-line reduction, triples | 30–60 min |
The gap between Hard and Evil is only four or five digits. That sounds small. In practice it is the difference between a grid that opens up after a few pairs and one where nothing moves until you spot a digit trapped in a single row of one box.
A Sudoku puzzle is only fair if it has one answer. Blank too many cells and a grid can have two valid solutions, both legal, both complete. That is not a harder puzzle. It is a broken one.
Our generator handles this the slow way, on purpose. It starts from a completed grid and tries to blank cells one at a time. After each attempt it counts the solutions. If the grid still has exactly one, the cell stays empty. If a second answer has appeared, the digit goes back. Removal stops when the tier's target is reached, or when no further cell can be cleared without breaking uniqueness.
That is why the Evil band is 24 to 27 rather than something lower. It is the floor this method reaches while keeping the answer unique.
It also matters for how the board treats you. Every digit you type is graded against the solution, and finishing the grid is checked against it too. With two valid answers, a player who reasoned correctly could be told they were wrong. One solution per grid is what makes that grading honest.
17 is the smallest number of givens that can still pin a single solution. Gary McGuire, Bastian Tugemann and Gilles Civario proved it in 2014 with an exhaustive computer search: no 16-clue Sudoku with a unique answer exists. It is a genuinely interesting result.
It does not make a good puzzle. Grids that sparse usually need very long candidate chains — the kind where you follow an implication ten cells deep and cannot tell whether you are reasoning or guessing. Most players stop enjoying a grid well before that point.
So be clear about what this page offers. Evil here means 24 to 27 givens with a verified single answer, which is the band where hard logic still feels like logic. If you specifically want a 17-clue grid, we do not deal one.
The order matters more at this level than at any other. Reaching for a rectangle pattern before you have filled in your notes wastes the work.
Our Sudoku tips and tricks page works through these one at a time with examples.
One Evil grid a day, the same grid for everyone, generated from the date. Finish it and your streak grows; the streak counts a day once, whichever tier you played. There is a Daily at Easy and Hard as well, so a day you do not have an hour to spare is not a day you lose the streak.
Go to today's Daily Sudoku.
Same engine, same rules, different clue counts. Switch from the difficulty menu at any time.
Yes. Evil Sudoku on TrySolitaire is free, with no download and no sign-up. It runs in your browser. You can install it as an app on any device, after which it works without an internet connection.
Between 24 and 27. The exact count varies from deal to deal. Hard gives you 28 to 32, Easy gives 36 to 40, and Beginner gives 42 to 46. Fewer givens means more cells you have to deduce, which is most of what makes a grid hard.
Yes, and it is checked rather than assumed. The generator blanks a cell only if the grid still has a single solution. If blanking a cell would allow a second answer, that cell stays filled. This matters because the board grades each digit you enter against the solution: with two valid answers, a correct entry could be marked wrong.
No. One solution means every empty cell is determined by the givens, so each digit can be reasoned out. What changes at this level is how far ahead you have to look. Singles alone will not finish an Evil grid: every one needs pointing pairs or box-line reduction, some need a naked triple, and an X-wing turns up now and then.
Around 30 to 60 minutes once you know the techniques, and longer while you are learning them. Hard grids run 15 to 30 minutes by comparison. The timer on the board is optional and can be switched off if it puts you off.
17 is the smallest number of givens that can still fix a single solution. McGuire, Tugemann and Civario proved it in 2014 with an exhaustive computer search, so no 16-clue puzzle exists. Grids that sparse are a mathematical curiosity more than a good game: they tend to need very long candidate chains, which most players experience as trial and error. The 24 to 27 band is where hard logic stays logic.
Evil is the usual name for the top tier, and it is what most players search for. Some sites label the same level Expert or Extreme. There is no shared standard behind the labels, so a given site's Evil is not always the same difficulty as another's — the clue count tells you more than the name does.
Yes. The print option generates a sheet of puzzles at the difficulty you pick, with the solutions on a separate page. Printed grids come from the same generator, so they carry the same single-solution guarantee.
24 to 27 givens, one answer, and no way to reach it except logic. Free in your browser.
Play Evil Sudoku Free Try Hard First