Hard Sudoku is where the puzzle stops being a scan-and-fill and becomes a logic problem. Every Hard puzzle on PuzzleCraft needs at least one advanced step, such as a naked or hidden triple, or box/line reduction, on top of pairs and pointing.
How it works: every PuzzleCraft Sudoku is built from scratch by a generator that fills a complete 9×9 grid and then removes numbers one at a time, checking with a solver after every removal that exactly one solution remains. You will never get a puzzle that needs guessing or has two answers.
Difficulty is rated by the solving techniques a puzzle needs, not just by how many numbers are given. Easy puzzles fall to singles alone. Medium adds naked pairs and pointing. Hard needs triples and box/line reduction. Expert asks for advanced patterns such as the X-Wing and XY-Wing.
Play right in the browser with a big touch-friendly number pad or your keyboard. Turn on Notes to pencil in candidates, and they disappear automatically when you place a number. Undo, redo, an eraser, row/column/box highlighting, matching-number highlights, optional mistake checking and a pausable timer are all built in. Your progress saves on your device, so you can come back to an unfinished grid later.
Stuck? The Hint Assistant teaches instead of just giving answers. The first hint points to the area to look at, the second names the technique, the third highlights the exact squares and explains the logic in plain English, and only the fourth fills in the number. Hints used appear on your results card.