Every puzzle in this app is a 27–29 clue grid with exactly one solution — verified in advance, so there's always a logical path through, never a guess required. "Hard" uses the same technique vocabulary as "Medium" — Naked and Hidden Pairs, Pointing Pairs/Triples, and the occasional Triple, nothing more exotic, no Y-Wings, no chains, no guessing — but leans on it roughly twice as often: about 6 non-Singles moves per puzzle on average, compared to 3 for Medium. Three out of four puzzles here need 5 or more. Same toolkit, used far more.
Import a puzzle
Paste 81 numbers, in almost any format: comma- or space-separated, a 9×9 grid, or one long string. Use 0 or . for empty cells — box-drawing separators (| and ---+---) are fine too.
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