Hard Sudoku — Notes, Triples and X-Wings

Hard Sudoku is rated 3.0 to 4.9 on the Sudoku Explainer scale (ER), the first band where a pattern spanning several units is required. Our classic hard grids hold 22 to 44 given digits (27.0 on average), so a puzzle with many clues can still be hard. What matters is where the givens sit, and with an average of 27 most cells start with several candidates.

What this level asks

Fill in candidates for the whole grid, then look for one structure that removes a digit from cells singles cannot reach. Expect a few of these moments per puzzle, each one opening a region. Hard is where casual solvers become serious ones: a difficult sudoku puzzle rewards patience, and notes are no longer optional.

Techniques you will meet

The tough tier starts here. X-Wing rates 3.2: it works on one digit spread across four cells, ignoring everything else in them. Swordfish rates 3.8. Naked and hidden triples sit at 3.6 and 4.0 and are the three-cell version of pairs. Wings come in toward the top of the band: Y-Wing, built from three cells with two candidates each, rates 4.2, and XYZ-Wing 4.4. Pairs rate 3.0, so they are the baseline here.

Tips for this level

• Keep notes accurate. One wrong candidate makes a valid pattern look false.
• For fish, count where a digit appears in each row or column: exactly two spots is the cue for an X-Wing.
• Look at cells with two candidates for wings.
• Run the stall loop: when stuck, retry the simplest technique you have not tried yet before reaching for a fancier one.
• Ask for a hint rather than guessing. A guess that happens to work teaches you nothing.

Next step

If wings and fish feel routine, Expert Sudoku brings chains. If triples confuse you, revisit Medium.