Hard Sudoku

Play free Hard Sudoku online with candidate pairs, locked candidates, and deeper multi-step deductions.

Play Hard SudokuGet the iPhone app

What to expect

Hard puzzles reward careful pencil marks and subset spotting. They remain human-solvable without trial-and-error or hidden guesses.

Techniques in this level

Naked PairHidden PairLocked Candidates

Hints stay progressive: see the pattern, understand why it works, then apply the result.

Other difficulties

Beginner

Build confidence with clear next moves.

Easy

A calm, quick logic workout.

Medium

Move beyond singles.

Hard

Work through pairs and intersections.

Expert

Find fish, wings, and precise eliminations.

Master

Follow coloring and logical chains.