Master Sudoku
Master is the top of our ladder. These puzzles resist every pattern from the easier tiers: singles, pairs, triples, fish, wings, coloring, all of it. What breaks them is chain logic, following a candidate’s consequences across the board until something gives. Set aside an hour and expect to use all of it.
One promise survives even here: no guessing. The chain is long, but it is logic the whole way.
What master means
Our solver grades every puzzle by the hardest technique required, and a master puzzle is one that stays locked until forcing chains come out. We verify each one falls to a chain of known human techniques before publishing. If our solver cannot finish a puzzle with human logic, you never see it: it gets discarded, no matter how interesting it looked.
That policy is the difference between hard and hostile. A master puzzle asks for everything you have; it never asks for luck.
Forcing chains
A forcing chain tests a candidate by following it. Take a cell with two candidates and trace both branches: if this cell is 1, that cell becomes 7, which makes another cell 4, and so on. When both branches force the same conclusion, that conclusion is simply true. When one branch collapses into contradiction, the candidate that started it is false.
Chains built from bivalue cells, like the one above, are the friendliest entry point: every step is forced because each cell only has one other option. Keep your notes immaculate before starting one. A single stale candidate sends the chain somewhere false, and the conclusion with it.
Advanced wings
Between the XY-wing and full chains sits a family of compact patterns worth knowing. The XYZ-wing adds a third candidate to the pivot, and its eliminations only hit cells that see all three pattern cells. The W-wing takes two separated cells with the same two candidates, connects them through a strong link on one digit, and eliminates the other digit from cells seeing both ends.
You can treat every one of them as a short forcing chain, and honestly, that is the healthiest way to think at this tier. The named patterns are compressed chains someone found often enough to label. When you spot an elimination through raw chain logic that you later learn had a name, you were doing it right.
Solving posture
A master puzzle is a long project, and the site is built for that. Your position, notes, timer and full undo history autosave on every action, one slot per difficulty, so a Tuesday puzzle can finish on Thursday. The pause button blurs the board to keep your time honest. Undo unwinds a failed chain in one step per action, and even a restart is one undo away if you confirm it and regret it.
Use hints without shame. On this tier the hint button is less a crutch than a tutor: it fills the cell a logical solver would take next, which often shows you where the chain you missed was anchored. The count lands on your completion screen, and nobody else sees it.
If a puzzle stalls completely, park it and open the technique reference. Rereading a pattern with a live position in your head beats rereading it cold. And when you want to remember what mortal puzzles feel like, expert will seem almost gentle from up here.
Frequently asked questions
What is the hardest sudoku technique?
Among techniques humans use, forcing chains sit near the top. You follow the consequences of a single candidate through a chain of cells until it either proves itself or collapses into contradiction. Master puzzles on this site require them; nothing below master does.
Are master puzzles actually solvable by a human?
Yes. Our generator verifies every master puzzle falls to a chain of known human techniques before it ships. None of them require trial and error, though they demand patience and complete pencil marks.
How long does a master sudoku take?
An hour or more is normal, and nobody finishes one in ten minutes. Your game autosaves on every move, so you can close the tab mid-solve and pick the same board up tomorrow.
Is master the same as evil sudoku?
Evil, extreme, diabolical, master: the puzzle world has many names for its top tier. Ours is defined by the technique it forces. Master means forcing chains, verified by our solver before a puzzle ships, so the label describes the logic waiting inside.
Other difficulties
- Easy sudokuSolvable with scanning and singles. The right place to learn the habits.
- Medium sudokuIntroduces pencil marks, locked candidates and naked pairs.
- Hard sudokuHidden pairs, triples and X-wings. Full pencil marks recommended.
- Expert sudokuXY-wings, swordfish and coloring. Logic all the way, no guessing.