Stuck on a Hard or Expert Sudoku? The Technique You Need Next

When singles run out: the techniques that decide Hard, Expert, Master and Extreme puzzles, counted across our 60,000-puzzle bank, and where to learn each one.

Updated 2026-11-05

First, make sure you are really stuck

Before reaching for a new technique, check that every single has been found: go through each digit across the boxes once more, and update your notes after every placement. Then check for a mistake. A square with no possible digit, or a digit with no place left in some row, column or box, means a wrong entry earlier, and no technique will get you past it.

What decides each level

We solved all 60,000 puzzles in our app's bank with its hint engine, which always takes the easiest step available, and recorded the hardest step each puzzle needed. That step decides the puzzle's level. The tables below show, level by level, which technique was that hardest step and in what share of the puzzles.

Hard: notes and intersections

Hard is the first level where singles are not enough. In 59.6% of our Hard puzzles the hardest step is a pointing pair: inside a box, the notes for one digit all sit in one row or column, so that digit can be removed from the rest of that row or column outside the box. Next come the naked pair (18.3%) and the box/line reduction (13.1%).

Hardest step	Share of puzzles
Pointing Pair	59.6%
Naked Pair	18.3%
Box/Line Reduction	13.1%
Hidden Pair	6.0%
Pointing Triple	2.2%
Naked Triple	0.8%
Hidden Triple	0.1%

Expert: the first patterns

Expert puzzles need a pattern that spans the grid. Most often it is a Skyscraper (55.1%) or a Y-Wing (30.3%). The X-Wing, the pattern most guides teach first, is the hardest step in only 3.7% of them, so look for a Skyscraper and a Y-Wing first.

Hardest step	Share of puzzles
Skyscraper	55.1%
Y-Wing	30.3%
Empty Rectangle	5.9%
Simple Coloring	4.4%
X-Wing	3.7%
Swordfish	0.5%
Naked Quad	< 0.1%

Master: chains and wings

Master puzzles are decided by chains and wings: an XY-Chain in 59.3% of them and a W-Wing in 28.1%. Both start from squares with exactly two notes, so those squares are the place to look.

Hardest step	Share of puzzles
XY-Chain	59.3%
W-Wing	28.1%
X-Chain	6.1%
XYZ-Wing	5.0%
Grouped Two-String Kite	0.9%
Two-String Kite	0.4%
WXYZ-Wing	0.1%

Extreme: almost locked sets

Extreme puzzles need an almost locked set: a group of squares in one row, column or box that hold one more possible digit than they have squares. ALS-XZ is the hardest step in 86.3% of them, and a unique rectangle in most of the rest (12.1%). No puzzle in our bank needs anything harder.

Hardest step	Share of puzzles
ALS-XZ	86.3%
Unique Rectangle	12.1%
Finned X-Wing	1.2%
Finned Swordfish	0.4%
ALS-XY-Wing	< 0.1%

How to look for the next technique

Fill in all notes first: every technique from Hard on works on them.
Try the techniques in each table's order, the most common first.
For X-Wings, Skyscrapers and other one-digit patterns, look at one digit at a time across the whole grid.
For pairs, Y-Wings, W-Wings and chains, look at the squares with exactly two notes.
If you still cannot find it, ask our solver or the app for a hint: it names the technique and shows where it is on your grid.

Practice

Every Find the Mistake puzzle on this site has exactly one wrong digit, and you can play each board right on its page.

Play the puzzles →