Expert Sudoku

The highest tier — the kind of puzzle some sites label evil. Grids that shrug off the entire repertoire of the lower levels and yield only to the most extended techniques: patterns spanning three lines, and candidate chains that travel the whole board. Free, no sign-up, playable offline.

The top of the ladder

An expert sudoku is not a slower hard one. It's a puzzle where, at some point, pairs, triples and X-Wings simply stop being enough. The game stalls, your pencil marks are complete, and the next move exists — but it has to be found at a wider scale. This is the level for players who know the intermediate techniques by heart and want puzzles that genuinely test them.

Here too, the tier is assigned by the internal solver: a puzzle enters this level only if it requires at least one of the two techniques below.

Swordfish and simple coloring

The Swordfish extends the X-Wing from two lines to three: a candidate confined, across three rows, to the same three columns — and those three columns are swept clean everywhere else. If you've internalised the X-Wing rectangle, you'll recognise the same logic, at a scale that demands a more systematic search.

Simple coloring works on chains instead: you follow one candidate through its strong links, alternating two "colors", until the chain itself produces a contradiction or a confirmation. It's the most abstract technique in the repertoire — and the one that most rewards disciplined pencil marks.

Verified by the solver: logic, never luck

This promise holds at every level, and it matters most here: every expert puzzle has been solved by the internal solver using human techniques only, from singles to coloring. No puzzle requires guessing or backtracking through hypotheses. If you're stuck, the step is there — it's just well hidden.

If you get stuck

It happens, and it's part of the level. The in-game hint first tells you the name of the applicable technique and where to look, without revealing the move — often that's all it takes. To refresh the fundamentals, there's the technique guides index; to catch your breath without dropping too far, hard sudoku.