What is Extreme level?
Extreme puzzles stall even with basics, pairs, pointing, X-Wing, Swordfish and XY-Wing. The program checks this for every puzzle, and each still has exactly one solution.
Beyond this point you need deeper reasoning, such as following chains of candidates.
Techniques for this level
- X-Wing: One number, two rows, same two columns: clear it from those columns
- Swordfish: One number, three rows, same three columns: clear it from those columns
- XY-Wing: Pivot and two pincers clear their shared number
All Sudoku strategies →
About this level
Is Extreme the hardest Sudoku in the world?
No. Above it is Evil, the hardest level on puzuru, selected from Extreme. Famous 'world's hardest' puzzles need even longer chains of reasoning. Extreme puzzles stall with every technique up to XY-Wing, and each has exactly one solution.
What about diabolical or impossible Sudoku?
Diabolical, impossible and very hard are names other sites use for their top tiers. There's no shared standard. None of puzuru's puzzles is impossible: each has exactly one solution.
Difficulty levels
| Level | Given numbers | What it takes |
|---|
| Easy | 40 | Fill cells that have only one possible number |
| Medium | 32–33 | Same technique, fewer clues, more searching |
| Hard | 26–28 | Use notes; pairs and pointing at most |
| Expert | 26 or fewer | Basics always stall; pairs or pointing required |
| Master | 28 or fewer | Pairs stall; X-Wing or XY-Wing required |
| Extreme | 26 or fewer | Even X-Wing stalls |
| Evil | 26 or fewer | The Extreme puzzles that need the deepest reasoning. The hardest level |
How to play
1. Pick a levelChoose one of seven levels from Easy to Evil. You get a new puzzle each time.
2. Fill in numbersTap a cell, then a number. Each row, column and 3x3 box must contain 1 to 9 exactly once.
3. Complete the gridUse Notes to pencil in candidates. Wrong numbers turn red.
Full rules and how to play →
How to solve an Extreme Sudoku when you're stuck
Start by getting every candidate on the board. Switch on the "fill all notes" button in Settings and tap All notes, or pencil them in yourself with Notes. Then sweep again for the easy wins: a cell with one candidate left, a number with only one spot in a row, column or box, and naked or hidden pairs. Placing a correct number clears it from the notes in its row, column and box, so check for new singles each time you place one.
Next, look at how candidates line up. Pointing: if a number's only spots in a box sit in one row or column, remove it from the rest of that line. Then check each number for an X-Wing or Swordfish, and look for an XY-Wing: a pivot AB that sees two cells AC and BC, which lets you remove C from any cell that sees both of them. Every puzzle at this level stalls even after all of these, so a stall doesn't mean you made a mistake. It means it's time for chains.
A chain is "if this, then that" followed through several cells. One kind, a forcing chain, starts from a cell with two candidates, say 4 or 7. Follow what happens if it's 4, then what happens if it's 7. If both paths remove the same candidate from some cell, that candidate is gone for good. An XY-Chain is a single line of two-candidate cells, each seeing the next and sharing one number with it. If the chain starts and ends on the same number, one of the two end cells must hold it, so you can remove that number from any cell that sees both ends. You never need to guess blindly, though the hardest steps can take long chains.
Extreme Sudoku online or on paper
You can play Extreme Sudoku right here on a phone, tablet or computer. On screen you get Notes, an optional All notes button, Undo, and wrong numbers that turn red (you can turn that off in Settings, though the Mistakes counter still goes up). Hint flags a wrong number first. Otherwise it highlights the row, column or box where the next step is, and when that step needs deeper reasoning, it offers to fill in a cell for you.
Prefer pencil and paper? The printable page makes Extreme sheets with 1, 2 or 4 puzzles per page and optional answer pages, and there are two ready-made Extreme PDFs with answers. Paper is handy for long chains, since you can circle candidates and draw lines between cells. On screen, notes stay tidy and Undo takes back moves one tap at a time. Plenty of players do both: print a few to take along, then come back here for a fresh puzzle and your stats.
FAQ
How long does an Extreme Sudoku take?
It varies a lot from puzzle to puzzle and from player to player, so there's no typical time. One stubborn chain can take longer than the rest of the grid. Open Stats from the menu to see how many Extreme puzzles you've solved, plus your best and average times, even if you keep the timer hidden. Tap Show time to see the clock while you play.
Do I need to guess on Extreme?
No. When pairs, fish and XY-Wing run out, use chains instead of guesses: trace what each candidate of a two-candidate cell forces, and keep only what both paths agree on. If you're truly stuck, Hint can fill in a cell for you.
What's the difference between Extreme and Master?
Master puzzles stall after pairs and pointing but can be finished with X-Wing, Swordfish or XY-Wing. Extreme puzzles stall even with all of those, so you'll need chains or other deeper reasoning.
Is it free?
Yes. All seven levels are free. No sign-up.
Does every puzzle have one solution?
Yes. Each puzzle is checked by the program to have exactly one solution.
Will I lose my progress if I leave?
No. Open the same level on the same device and browser to continue. One game is saved per level.
What is the "???" button?
It's a secret stage with 3 special puzzles you won't find anywhere else (3 levels). Share, or enter the password, to open it. The password is in the share text and changes every Monday.
What are the daily stamps?
You get one stamp on each day you play. The days don't need to be in a row. Every 7th stamp is gold: it unlocks a board theme and gives you a 🎟️ mistake pass. Your stamps are saved only in this browser (no sign-up).
What is the 🎟️ mistake pass?
It lets you undo a mistake. You get one every day (use it that day) and one with each gold stamp (you can keep these). Tap the button that appears when you make a mistake. Your time still counts for the ranking.
Are there ads?
We never interrupt you with ads while you're solving a puzzle.
Can I play on my phone?
Yes. No install needed. On a computer you can also use number keys, arrow keys and N to toggle notes.
