Expert Sudoku
Expert sudoku trades local logic for board-wide sight. The techniques that define this tier connect cells that share no row, column or box, and finding them means reading the whole candidate picture at once. Every puzzle here demands at least one of them: an XY-wing, a swordfish, a skyscraper or coloring.
And every puzzle still falls to pure logic. That claim gets tested by software before a single person plays it.
How expert is graded
Our generator attempts each candidate puzzle with a ladder of human techniques and files the puzzle under the hardest rung it touched. Expert puzzles resist everything through X-wings, then yield to the patterns on this page. Puzzles that need full forcing chains get filed under master instead, so the ceiling here is real.
Work with complete pencil marks from the start. Auto notes fills them in one tap, and auto-remove keeps them truthful as you place digits. Expert patterns are invisible without them.
The XY-wing
Three bivalue cells make a pincer. A pivot holding two candidates sees two wings, each sharing one of the pivot’s digits, both sharing a third digit Z between them. Whichever way the pivot resolves, one wing becomes Z. So any cell that sees both wings cannot be Z.
Hunt XY-wings by cataloguing bivalue cells; there are rarely more than a dozen. Take each as a pivot and check what its bivalue neighbors share.
The swordfish
An X-wing stretched to three rows. One candidate occupies at most three columns across exactly three rows, with the columns overlapping into a shared set of three. The digit must land once in each of those columns, inside those rows, so every other copy of the candidate in the three columns dies.
Swordfish reward patience over cleverness. Pick a digit, mark its possible rows, and check whether three of them stay within three columns. Most digits fail fast; the one that fits pays for the rest.
Skyscrapers and coloring
Both techniques run on strong links: units where a candidate has exactly two possible homes, meaning one of the two must be true. A skyscraper takes two strong links in parallel lines that share one end line. The shared ends cannot both be true, so at least one far end is true, and any cell seeing both far ends loses the candidate.
Coloring chains the same idea further: alternate two colors along every strong link for one digit, and any outside cell that sees both colors loses the digit. If one color ever collides with itself inside a unit, that entire color is false. When a single strong-link deduction is not enough, color the whole digit and let the chain do the work.
Pacing yourself
Expert solves run 30 minutes to an hour and more, and early ones stretch longer while the patterns are new. The clock pauses itself whenever you leave the tab, on screen or not, and your whole position autosaves every move, notes and history included. Walking away mid-solve costs nothing.
A practical tip: work one digit at a time when pattern hunting, and say the counts to yourself. Two in this row, two in that column. Strong links are the raw material of every technique on this page, and counting is how they surface. The complete reference for each pattern sits on the how to play page, and when even these feel routine, master sudoku removes the last safety rail.
Frequently asked questions
Can every sudoku be solved without guessing?
Every sudoku on this site can. We grade each puzzle by running it through a solver that only uses human techniques, and anything it cannot finish never gets published. Expert puzzles included: the logic path exists, it is just harder to see.
Do I need notes for expert sudoku?
Yes, realistically. Expert techniques operate on candidates rather than placed digits, so you cannot even see an XY-wing without marks on the board. Use Auto notes to fill them in, then let the techniques do the pruning.
What makes expert harder than hard?
Hard techniques look at one unit at a time. Expert patterns like the XY-wing and skyscraper span the whole board and connect cells that share no row, column or box. Spotting them means holding more of the board in view at once.
How long does an expert sudoku take?
From 30 minutes to over an hour, and the first few can take longer while the patterns are new. The clock stays hidden unless you switch it on, and it pauses when you leave the tab, so a long solve stays an honest one.
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.
- Master sudokuForcing chains. The hardest puzzles we generate.