--- title: "Stuck on Hard Sudoku? The Technique You Need Next | Sudoku Flow" description: "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." url: https://sudokuflow.com/guides/stuck-on-hard-sudoku/ language: en last_modified: 2026-11-05 --- [Sudoku guides](https://sudokuflow.com/guides/) # 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 ## Quick answer If no row, column or box gives you a single, the puzzle needs a technique that works on notes. On Hard, that is most often a pointing pair, otherwise a naked pair or a box/line reduction. On Expert, look for a Skyscraper or a Y-Wing before an X-Wing. Master puzzles need chains and wings, and Extreme puzzles an almost locked set or a unique rectangle. - First make sure every single has been found and nothing is wrong. - Hard: a pointing pair in most puzzles. - Expert: a Skyscraper or a Y-Wing far more often than an X-Wing. - Master: XY-Chains and W-Wings, from squares with two notes. - Extreme: ALS-XZ, otherwise a unique rectangle. ## 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](https://sudokuflow.com/lessons/pointingPair/) | 59.6% | | [Naked Pair](https://sudokuflow.com/lessons/nakedPair/) | 18.3% | | [Box/Line Reduction](https://sudokuflow.com/lessons/boxLineReduction/) | 13.1% | | [Hidden Pair](https://sudokuflow.com/lessons/hiddenPair/) | 6.0% | | [Pointing Triple](https://sudokuflow.com/lessons/pointingTriple/) | 2.2% | | [Naked Triple](https://sudokuflow.com/lessons/nakedTriple/) | 0.8% | | [Hidden Triple](https://sudokuflow.com/lessons/hiddenTriple/) | 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](https://sudokuflow.com/lessons/skyscraper/) | 55.1% | | [Y-Wing](https://sudokuflow.com/lessons/yWing/) | 30.3% | | [Empty Rectangle](https://sudokuflow.com/lessons/emptyRectangle/) | 5.9% | | [Simple Coloring](https://sudokuflow.com/lessons/simpleColoring/) | 4.4% | | [X-Wing](https://sudokuflow.com/lessons/xWing/) | 3.7% | | [Swordfish](https://sudokuflow.com/lessons/swordfish/) | 0.5% | | [Naked Quad](https://sudokuflow.com/lessons/nakedQuad/) | < 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](https://sudokuflow.com/lessons/xyChain/) | 59.3% | | [W-Wing](https://sudokuflow.com/lessons/wWing/) | 28.1% | | [X-Chain](https://sudokuflow.com/lessons/xChain/) | 6.1% | | [XYZ-Wing](https://sudokuflow.com/lessons/xyzWing/) | 5.0% | | [Grouped Two-String Kite](https://sudokuflow.com/lessons/groupedTwoStringKite/) | 0.9% | | [Two-String Kite](https://sudokuflow.com/lessons/twoStringKite/) | 0.4% | | [WXYZ-Wing](https://sudokuflow.com/lessons/wxyzWing/) | 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](https://sudokuflow.com/lessons/alsXZ/) | 86.3% | | [Unique Rectangle](https://sudokuflow.com/lessons/uniqueRectangle/) | 12.1% | | [Finned X-Wing](https://sudokuflow.com/lessons/finnedXWing/) | 1.2% | | [Finned Swordfish](https://sudokuflow.com/lessons/finnedSwordfish/) | 0.4% | | [ALS-XY-Wing](https://sudokuflow.com/lessons/alsXYWing/) | < 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 →](https://sudokuflow.com/puzzles/) ## Sudoku guides - [How to Find a Mistake in Sudoku](https://sudokuflow.com/guides/find-a-mistake/) - [7 Common Sudoku Mistakes and How to Avoid Them](https://sudokuflow.com/guides/common-mistakes/) - [Why Won't My Sudoku Solve? A Checklist](https://sudokuflow.com/guides/sudoku-wont-solve/) - [Naked Single vs Hidden Single](https://sudokuflow.com/guides/naked-single-vs-hidden-single/) - [Pointing Pair vs Box/Line Reduction](https://sudokuflow.com/guides/pointing-pair-vs-box-line-reduction/) - [X-Wing vs Swordfish](https://sudokuflow.com/guides/x-wing-vs-swordfish/) - [How to Start a Sudoku: The First Five Minutes](https://sudokuflow.com/guides/how-to-start-sudoku/) - [Sudoku Tips That Actually Work (and Is There a Formula?)](https://sudokuflow.com/guides/sudoku-tips/) - [How to Teach a Child Sudoku: 4×4, Then 6×6, Then 9×9](https://sudokuflow.com/guides/teach-kids-sudoku/) - [Can Every Sudoku Be Solved Without Guessing?](https://sudokuflow.com/guides/solve-without-guessing/) - [What each Sudoku difficulty level asks of you](https://sudokuflow.com/data/sudoku-difficulty-levels/) - [Sudoku facts](https://sudokuflow.com/guides/sudoku-facts/) - [Sudoku checker](https://sudokuflow.com/tools/sudoku-checker/) - [Sudoku for kids](https://sudokuflow.com/printables/kids/) - [Find the Mistake Sudoku](https://sudokuflow.com/find-the-mistake/) ![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png) ## Want more boards like this? We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number. [App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite) Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.