Evil sudoku: the hardest level

Evil is the ceiling. It covers every puzzle whose hardest requirement goes beyond X-Wing — in our pools that's usually XY-Wing(three cells, each sharing a digit with the other two, that combine to rule out a candidate none of them touch directly) or Swordfish(X-Wing's logic stretched across three rows and three columns instead of two). Occasionally a puzzle lands here because it needs a deeper chain of deductions that doesn't reduce to any single named technique at all.

That last point is worth being honest about: our logical solver models ten named techniques, from naked singles up through XY-Wing and Swordfish. A puzzle that resists all ten still has a unique solution — our generator guarantees that — but you may need backtracking-style trial and error, or a technique we haven't named yet, to finish it without a hint.

Who evil suits

Solvers who want to be stuck for a while, on purpose. This isn't the level to reach for if you want a relaxing ten minutes — it's the one to reach for when you specifically want to be tested.

If a puzzle genuinely won't move

Use the hint button. It runs the same logical solver we use to grade every puzzle, so if a step exists, it will find it and explain it — the same way it does on every other level. There's no shame in using a few hints on this tier; the "hints used" count on the completion screen is informational, not a score.

Want the same exact puzzle to go back to, or to challenge someone else to? Every board here has a permanent link — use the share button once you've finished, or on the daily puzzle page for one that resets every day.