SuuudokuuuHard Sudoku Puzzles
Updated
Hard Sudoku is a difficulty tier that starts at 26 clues out of 81 cells and is defined by what a subset-only solver cannot finish: every board in the tier has been run through a solver equipped with every intersection and every subset up to the hidden quad, and kept only because that solver got stuck. What breaks the deadlock is a fish — X-Wing, swordfish, jellyfish and their finned and sashimi variants — or a wing: XY-Wing, XYZ-Wing and W-Wing.
Play Hard Sudoku nowWhat makes a puzzle Hard
A fish looks at one digit across several lines at once. The X-Wing is the smallest: a digit confined to the same two columns across two rows can be erased from the rest of those columns, because whichever row ends up holding it, the columns are already fixed. A swordfish stretches the same idea over three lines and a jellyfish over four. Finned and sashimi variants relax the base pattern by allowing one extra candidate that still supports a smaller, safe elimination once you account for it — and in our sample they fire far more often than the textbook shapes do. Wings work differently: an XY-Wing links three bivalue cells so a candidate shared between two of them can be erased wherever both can see, XYZ-Wing gives the pivot that candidate too, and W-Wing joins two matching bivalue cells through a strong link on one shared digit. Hard is capped at the W-Wing: a board that still will not move after every fish and wing has been tried is a Nightmare board, not a Hard one.
How hard is it, honestly
Our sample of 40 Hard boards measures SE (Sudoku Explainer) 3.4 to 4.4 — squarely in the range the solving community associates with fish and wing patterns, and well below the chain territory above 7. The most common hardest step is the XY-Wing, and the hardest anything in the sample reached is the W-Wing. This is where casual solvers start reaching for a hint: fish and wings are easy to describe and genuinely hard to see on a live board, so expect a noticeably longer, more deliberate solve than Medium asks for. See the sudoku difficulty rating guide for the full per-tier data.
Where to go next
Ready to chain eliminations together instead of spotting shapes? Move up to Nightmare Sudoku, or step back to Medium Sudoku for an intersections-and-subsets puzzle. Prefer paper? Download the printable Hard sudoku PDF. See the technique index, the how to play guide, every tier on the Sudoku difficulty levels hub, or head home.
Hard Sudoku FAQ
What techniques do I need for Hard sudoku?
Everything Medium needs, plus at least one fish or wing pattern: X-Wing, swordfish, jellyfish, their finned and sashimi variants, XY-Wing, XYZ-Wing or W-Wing. One of those is always required, because a board that does not need one is graded Medium instead.
How many clues does a Hard sudoku have?
26 clues out of 81 cells — only one fewer than Medium, which is exactly why the tier is defined by the techniques it requires rather than by its clue count.
What is a finned fish in sudoku?
An almost-fish: the rows or columns line up as an X-Wing or swordfish except for one or two extra candidates, the fin. The elimination still holds, but only in the cells that both the fish and the fin can see.
Is Hard sudoku harder than Nightmare?
No. Hard tops out at the W-Wing; Nightmare starts where Hard stops and runs up to alternating inference chains. The two tiers are separated by a technique boundary, not by a clue count.