Extreme Sudoku Puzzles
Extreme is the hardest level on this site. Every board starts with only 22 or 23 givens, leaving 58 or 59 cells to solve, and the generator rejects any puzzle that gives in to singles and pairs alone. Expect locked candidates and naked pairs as a matter of course, and on roughly a third of boards something more: X-Wing, XY-Wing, Swordfish or a similar pattern that spans the whole grid. The single-solution guarantee still holds. There is always a logical path; it is just well hidden.
What an Extreme board feels like
The opening is thin. You may place two or three digits by scanning and then nothing at all until the candidate grid is complete. The middle game is a hunt for eliminations rather than placements, and a single elimination can be the key that unlocks ten cells in a row. The finish, as always, is fast. Patience in the first fifteen minutes is what separates a solve from a reset.
Extreme Sudoku techniques
X-Wing
Look for a digit with exactly two candidate cells in each of two different rows, where those four cells form the corners of a rectangle. The digit must sit on one diagonal of that rectangle, so it can be removed from every other cell in the two columns. The same pattern works with columns as the base and rows as the cover.
XY-Wing
Three cells with two candidates each, arranged so that a pivot cell holding XY sees one cell holding XZ and another holding YZ. Whichever value the pivot takes, one of the wings becomes Z, so any cell that sees both wings cannot be Z.
Swordfish
The X-Wing idea extended to three rows and three columns: if a digit's candidates in three rows are confined to the same three columns, the digit can be cleared from those columns outside the three rows.
Naked and hidden triples
Three cells in a unit whose candidates together cover only three digits lock those digits into those cells; three digits that appear only in three cells of a unit lock those cells to those digits. Both are common on Extreme boards and easy to miss.
Extreme Sudoku tips and strategies
- Complete the candidate grid before you look for any pattern. Advanced techniques are only as reliable as the notes they run on.
- Work one digit at a time when hunting for X-Wings and Swordfish; look for rows where the digit has exactly two or three candidates.
- Use hints as a diagnostic. If a hint reveals a digit you had ruled out, your notes have an error somewhere upstream.
- Take a break and come back. Pause stops the clock and hides the board, and your game is saved in the browser.
Not quite there yet?
Master Sudoku uses pairs and locked candidates without the grid-spanning patterns, and Expert Sudoku is the best place to make hidden singles second nature before tackling Extreme. For the full reasoning behind X-Wing, XY-Wing and Swordfish, see the Sudoku techniques guide.
Frequently asked questions
How many givens does an Extreme Sudoku have?
22 or 23, the fewest of any level here. That leaves 58 or 59 cells to fill.
Which techniques do Extreme puzzles need?
Locked candidates and naked pairs on every board, plus advanced patterns such as X-Wing, XY-Wing or Swordfish on roughly a third of them.
Is guessing ever required on Extreme?
No. Every board is verified to have exactly one solution, so a purely logical path always exists, though it can be long and may need several eliminations before a digit can be placed.
How long does an Extreme Sudoku take?
Longer than any other level here: 58 or 59 empty cells, and much of the work is eliminating candidates rather than placing digits. We do not have a reliable average to quote, and times vary widely. Your game is saved automatically, so you can split a puzzle across several sessions.
Is Extreme the hardest Sudoku level?
It is the hardest level on this site. Puzzles that need even deeper chains exist, but they are rare and mostly hand-made; Extreme boards here already require X-Wing-class patterns on roughly a third of games.