Diabolical Sudoku: Hard Logic

Diabolical Sudoku is a no-nonsense sudoku app built for one thing: hard puzzles.
If easy sudoku has stopped being fun, this is for you—every puzzle is chosen to need real techniques like X-Wing, XY-Wing, and Swordfish.

■ Three difficulties
・Hard … solvable by logic alone, with real bite
・Expert … advanced techniques required
・Diabolical … X-Wing / XY-Wing / Swordfish-class stumpers

■ Highlights
・Step-by-step explanations … stuck on a puzzle? See which technique cracks which cell, one move at a time
・One unique solution … no guessing, ever. Pure logic always gets you there
・Controls your way … pick your input order (digit-first or cell-first) and your memo style
・Pencil marks, auto-candidates, highlighting, and reset
・Auto-save, with clear status and solve times recorded
・No interruptions … no full-screen ads breaking your concentration

One good puzzle at a time. Chase that "I solved it!" feeling, again and again.