Difficulty · Hard
Hard Sudoku — Free Difficult Puzzles
Hard Sudoku is where scanning alone stops working. Every puzzle demands full notes and intermediate techniques — pointing pairs, naked pairs, box-line reduction — but stays fully solvable by pure logic.
24–29 starting clues, one unique solution.
Full notes workflow with Snyder notation support.
Verified times on the Hard leaderboard.
Undo, hint, and validate tools when you're stuck.
Techniques for hard Sudoku
Learn pointing pairs, naked pairs, and box-line reduction — the three techniques that unlock 90% of hard puzzles. Our advanced strategies guide covers each with examples.
Ready for Evil?
If you finish hard puzzles under 10 minutes, Evil Sudoku is your next challenge. It's where X-Wing, Swordfish, and forcing chains come out.
Frequently asked questions
How do I solve hard Sudoku puzzles?
Hard Sudoku requires notes plus intermediate techniques: pointing pairs, naked pairs, hidden pairs, and box-line reduction. See our advanced strategies guide for details.
How long should a hard Sudoku take?
Most solvers finish a hard puzzle in 10–20 minutes. Under 8 minutes is expert territory.
Are hard Sudoku puzzles always solvable by logic?
Yes. Every SodokuDX puzzle has exactly one solution reachable by pure logic — no guessing needed.