Hard sudoku: play free online
Hard puzzles start with 24–29 given numbers and are solved with Naked Pair, Hidden Pair, Naked Triple, and Hidden Triple, without guessing. Fill in the grid below; if you get stuck, press Hint to see the next move and why it works.
Type a number into an empty square. Your progress is saved in this browser.
Turn on JavaScript to play here, or open the free app in your browser.
About Hard puzzles
Every puzzle on this page was generated and checked by the same solver that grades the puzzles in the Sudoku AI Coach app:
- It has exactly one solution.
- It starts with 24–29 given numbers.
- It can be solved with Naked Pair, Hidden Pair, Naked Triple, and Hidden Triple and the easier techniques before them, with no guessing.
If a technique is new to you, open its page to see an example, then come back and look for it in the grid.
Frequently asked questions
Is it free to play?
Yes. All puzzles and hints on this site are free, with no sign-up. Your progress stays in your own browser and is not sent anywhere.
What do I need to solve Hard puzzles?
Naked Pair, Hidden Pair, Naked Triple, and Hidden Triple. Each technique name links to a page that explains it with an example, and the hint button shows exactly where it applies.
Do the puzzles need guessing?
No. Every puzzle was checked to have one solution that can be reached by logic alone.
How does the hint work?
It finds the easiest next move and shows the squares and the reasoning behind it, without filling the square for you. Press it again after you place the number to get the next one.
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