Hard Sudoku Online

Intermediate techniques required, naked pairs, hidden singles, pointing pairs.

Fresh puzzle every page load · Sunday, 14 June 2026

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72 The small number = how many of that digit are still left to place.

Tips for hard Sudoku

Enable Notes before you start. Hard puzzles require tracking candidates. Pencil marks aren't optional at this level.
Look for naked pairs. Two cells in a unit sharing exactly two candidates let you remove those digits from all other cells in that unit.
Use pointing pairs. If a candidate in a box is confined to one row or column, remove it from the rest of that line outside the box.
Use Undo freely. Hard mode rewards experimentation. Undo a chain of moves to backtrack and try a different path.

More ways to play

Five free puzzle games, one calm hub. No account, no app.

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Why play Sudoku?

A few minutes of logic a day is a genuine workout for memory, focus and pattern recognition.

Sharper memory

Holding candidate numbers in mind exercises working memory, the mental scratchpad you use all day.

Better focus

Sudoku rewards sustained attention. Regular solving builds the habit of staying with a problem.

Calm & flow

The quiet, deliberate pace is a low-stakes way to decompress, a small daily ritual worth keeping.

What makes a Sudoku hard?

Hard Sudoku puzzles give you only 28–32 clues, so simple scanning runs out quickly and you have to reason about candidates rather than certainties. Pencil marks stop being optional. They become the board you actually solve on.

Techniques that unlock hard puzzles

Naked pairs / triples: two or three cells in a unit sharing the same candidates let you eliminate those digits elsewhere in the unit.
Hidden pairs: two digits confined to the same two cells.
Pointing pairs (locked candidates): a digit confined to one row or column within a box, removing it from the rest of that line.

A typical hard puzzle takes an experienced solver 15–30 minutes. Use Notes liberally, lean on Undo to experiment safely, and keep the 3 hints for when you are genuinely stuck. Every puzzle is verified to have a single solution.

Frequently asked questions

Fewer given clues (28–32) and the need for techniques like naked pairs, hidden pairs and pointing pairs, rather than simple row/column/box scanning.

Usually 15–30 minutes for experienced solvers; beginners to the level may take longer. There is no time pressure unless you choose Challenge mode.

Yes, they are essential. Toggle Notes to pencil candidates; most hard techniques are pattern-spotting across those candidates.

Yes. Every puzzle is generated and verified to have exactly one solution reachable by deduction. No guessing required.

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Three mistakes

That's Challenge mode for you. Want to keep going on this same board in Relaxed mode instead?