Extreme Sudoku

The hardest level on the site

Extreme puzzles are accepted only when the solver needs two or more advanced techniques to finish, with 21 to 29 givens. There is no level above this one.

Two advanced steps is a different experience from one. After you find the first X-Wing or chain and take the eliminations it gives you, the grid moves a little and then closes again — and the second pattern is rarely the same type as the first.

How to work a grid this sparse

• Fill complete candidates before you place anything. On this level, guessing at pencil marks guarantees a wrong placement.
• Track digits with only two possible cells in a unit — every advanced pattern is built from them.
• Work one digit across the whole grid rather than one region across all digits.
• When you find an elimination, re-scan for singles before hunting again; one removal often cascades.

Still no guessing

Extreme does not mean trial and error. Every puzzle here was solved by the logical solver before it reached you, so a complete path exists that never requires a guess. If you find yourself branching on a maybe, there is a pattern on the board you have not spotted.

That is also the honest use of the hint button on this level: not to fill a cell, but to find out which technique you failed to see.

If Extreme is too much

Master asks for exactly one advanced pattern instead of two, and the technique trainer lets you drill a single pattern — X-Wing, XY-Wing, Swordfish — on puzzles built to contain it. Both are faster ways to get comfortable than grinding Extreme grids.