Hard · LDI v0
Play Hard Sudoku Online
Choose from three calibrated hard puzzles. New Game stays on Hard, and the Puzzle ID, difficulty score, and solving facts update with the board.
LDI v0
Verified puzzle facts
- Puzzle ID
LDI0-01cb0dcea7b0ea68bf57e4634a750ff0d862017f- Difficulty model
- LDI v0
- LDI score (0–100)
- 31
- Clue count
- 27
- Logical steps
- 54
- Hardest technique
- Hidden Single
Clue count is a board fact, not the difficulty verdict. The tier comes from this published LDI version.
What Hard feels like
A higher LDI score turns familiar singles into a longer search.
The current Hard catalogue is still completed with singles, but its verified LDI scores sit well above Medium. Useful placements are less visible and often appear only after several accurate updates elsewhere on the grid.
How to approach Hard
Keep candidates accurate and repeat the hidden-single scan in full.
Work in passes: update candidates, inspect every row, column, and box for a number with one remaining position, then scan the whole grid again. Use Check after a meaningful run of deductions rather than after every placement.
Daily Sudoku challenges
Hard Daily Sudoku challenges
Choose any available date, then select this difficulty to play a free, verified puzzle.
Why this tier
Hard is a calibrated result, not a label based on clue count.
The score reflects proof-checked techniques and logical steps. Clue count remains useful context, but it does not decide the tier by itself.