Hard Sudoku

Hard Sudoku strips the grid down to about 28 clues, so scanning alone won't finish it — you'll need candidate elimination. Play unlimited hard puzzles online, or print a set with answers.

What makes a Sudoku hard?

A hard Sudoku leaves only about 28 given numbers, so the easy singles run out fast and you have to track candidates. Expect to lean on naked pairs (two cells in a unit sharing the same two candidates, which lets you erase those digits elsewhere in the unit) and pointing pairs (a digit locked to one row or column inside a box, so it can be removed from the rest of that line). The puzzles never require guessing — every one is verified to have a single solution reachable by pure logic.

How to solve hard Sudoku

Turn on pencil marks and keep them honest. When two cells in a group show the same pair of candidates, remove that pair from their neighbours. When a digit inside a box can only sit on one line, sweep it off that line in the adjacent boxes. Work digit-by-digit rather than cell-by-cell and the grid opens up. Stuck? The in-game AI Hint explains the next logical step. For a full walkthrough see how to play Sudoku, or the solving-techniques guide.