This is your quick-reference guide to every Sudoku solving technique. Bookmark this page or print it out — when you are stuck mid-puzzle, scan the tables below to identify the technique you need. Minimal prose, maximum reference value.
Basic Techniques
These two techniques solve every easy puzzle and are the foundation of all Sudoku solving. Master them before learning anything else.
| Technique | What to Look For | Result | Guide |
|---|---|---|---|
| Naked Single | A cell with only one candidate remaining | Place that digit | Full guide → |
| Hidden Single | A candidate that appears in only one cell within a row, column, or box | Place that digit | Full guide → |
When to use: Every single solve, at every stage. Always check for singles before trying anything more complex.
Intermediate Techniques
These techniques are needed for medium and hard puzzles. They eliminate candidates rather than directly placing digits.
| Technique | What to Look For | Result | Guide |
|---|---|---|---|
| Naked Pair | Two cells in the same unit sharing the exact same two candidates | Eliminate those two digits from all other cells in the unit | Full guide → |
| Hidden Pair | Two candidates that appear in only the same two cells within a unit | Remove all other candidates from those two cells | Full guide → |
| Naked Triple | Three cells in a unit whose candidates are a subset of three digits | Eliminate those three digits from other cells in the unit | Full guide → |
| Hidden Triple | Three candidates confined to only three cells in a unit | Remove all other candidates from those three cells | Full guide → |
| Pointing Pair | A candidate in a box restricted to a single row or column | Eliminate that candidate from the rest of the row/column outside the box | Full guide → |
| Box-Line Reduction | A candidate in a row/column restricted to a single box | Eliminate that candidate from the rest of the box | Full guide → |
When to use: After exhausting all naked and hidden singles. Check for pairs first — they are the most common intermediate technique.
Advanced Techniques
These techniques appear in expert puzzles. They typically involve interactions across multiple rows, columns, or boxes.
| Technique | What to Look For | Result | Guide |
|---|---|---|---|
| X-Wing | A candidate in exactly two cells in each of two rows, and those cells share the same two columns (or vice versa) | Eliminate that candidate from the rest of the shared columns (or rows) | Full guide → |
| Swordfish | Like X-Wing but across three rows and three columns | Eliminate the candidate from the rest of the three shared columns (or rows) | Full guide → |
| XY-Wing | Three bivalue cells forming a pivot + two wings, each sharing one candidate with the pivot | Eliminate the candidate common to both wings from cells that see both wings | Full guide → |
| XYZ-Wing | Like XY-Wing but the pivot has three candidates instead of two | Eliminate the shared candidate from cells that see all three wing cells | Full guide → |
| Skyscraper | Two columns (or rows) each with a candidate in exactly two cells, sharing one endpoint row (or column) | Eliminate the candidate from cells that see both non-shared endpoints | Full guide → |
| W-Wing | Two identical bivalue cells connected by a strong link on one of their candidates | Eliminate the other shared candidate from cells that see both bivalue cells | Full guide → |
| Empty Rectangle | A candidate forming a cross-shaped pattern in a box with a strong link in a row or column | Eliminate the candidate from the intersection cell | Full guide → |
| Simple Coloring | A candidate’s strong links form a chain of alternating colors across the grid | If two same-colored cells see each other → that color is false; if a cell sees both colors → it loses the candidate | Full guide → |
When to use: When all intermediate techniques fail. Start with X-Wing — it is the most common advanced pattern.
Expert Techniques
These techniques are needed for evil puzzles and the hardest competition grids. They involve complex chains and rare patterns.
| Technique | What to Look For | Result | Guide |
|---|---|---|---|
| Chains | A sequence of strong and weak links between candidates across multiple cells | Eliminate candidates at the end of the chain based on inference | Full guide → |
| Unique Rectangle | Four cells forming a rectangle across two boxes with a candidate pattern that would create two solutions | Eliminate candidates that would produce the deadly pattern | Full guide → |
| Finned X-Wing | An X-Wing pattern with one extra candidate cell (the fin) in one of the rows/columns | Eliminate the candidate from cells that see both the fin and the X-Wing intersection | Full guide → |
| Jellyfish | Like Swordfish but across four rows and four columns | Eliminate the candidate from the rest of the four shared columns (or rows) | Full guide → |
| BUG | The grid has exactly one cell with three candidates and all others have one or two (Bivalue Universal Grave) | The three-candidate cell must take the digit that appears three times in its row/column/box intersections | Full guide → |
| ALS (Almost Locked Sets) | Two groups of cells where each is almost locked (n cells with n+1 candidates) sharing a restricted common candidate | Eliminate candidates seen by both ALS groups | Full guide → |
When to use: Only after exhausting all advanced techniques. These are rare but essential for the hardest puzzles.
Quick Decision Tree
When you are stuck, follow this flowchart from top to bottom. Do not skip steps.
Step 1 → Check for Naked Singles Scan every cell. Is there any cell with only one candidate? If yes, place it and restart from Step 1.
Step 2 → Check for Hidden Singles For each row, column, and box: is there a candidate that appears in only one cell? If yes, place it and restart from Step 1.
Step 3 → Check Your Pencil Marks Before going further, verify your candidates are correct. A single error here will block all progress. Re-derive candidates for any suspicious cells.
Step 4 → Check for Naked Pairs / Hidden Pairs Look for two cells in a unit with the same two candidates (naked pair) or two candidates confined to the same two cells (hidden pair). Eliminate accordingly, then restart from Step 1.
Step 5 → Check for Pointing Pairs and Box-Line Reduction Is a candidate in a box limited to one row or column? That is a pointing pair. Is a candidate in a row/column limited to one box? That is box-line reduction. Eliminate and restart from Step 1.
Step 6 → Check for Triples Same logic as pairs but with three cells and three candidates. Check for naked triples and hidden triples.
Step 7 → Check for X-Wing For each candidate, check every pair of rows: does the candidate appear in exactly two cells in each row, and do those cells share the same two columns? If yes, apply X-Wing elimination.
Step 8 → Check for Coloring / Skyscraper / W-Wing Try simple coloring on each candidate. Check for skyscrapers and W-Wings. These single-digit techniques often break puzzles that resist fish patterns.
Step 9 → Check for Wings (XY-Wing, XYZ-Wing) Look for bivalue pivot cells connected to two wing cells. Apply XY-Wing or XYZ-Wing eliminations.
Step 10 → Check for Chains and Expert Patterns If nothing above works, look for chains, unique rectangles, finned X-Wings, ALS, and BUG patterns.
Step 11 → Take a Break If you have thoroughly checked Steps 1–10, walk away for five minutes. Fresh eyes catch what tired eyes miss. Return and restart from Step 1.
Common Patterns to Memorize
These are the three most frequent “stuck points” and the techniques that typically break them.
Stuck Point 1: Grid Feels Solved but Several Cells Remain
What is happening: You have placed many digits but a cluster of empty cells remains with multiple candidates each.
Likely solution: You have missed a hidden single or a hidden pair. Re-scan every row, column, and box for candidates that appear in only one or two cells. Focus on the units that intersect with the stuck cluster.
Stuck Point 2: Pencil Marks Show Lots of Pairs but No Singles
What is happening: Many cells have two candidates, but no cell has one. No naked singles exist.
Likely solution: Look for naked pairs that eliminate candidates from other cells, which then creates singles. Also check for pointing pairs — they are frequently overlooked and produce cascading eliminations. If the grid is very pair-heavy, watch for BUG patterns or XY-Wings.
Stuck Point 3: No Eliminations from Any Technique You Know
What is happening: You have checked singles, pairs, and basic intersection techniques. Nothing fires.
Likely solution: This almost always means you need a fish pattern (X-Wing, Swordfish) or coloring. Pick a candidate that appears frequently and check for X-Wing shapes across rows and columns. If that fails, try coloring that candidate’s strong links. If you are on a hard puzzle, one of these will almost certainly work. On expert or evil puzzles, you may need chains or wings.
Difficulty Cheat Sheet
Use this table to know which techniques each difficulty level requires.
| Difficulty | Techniques Needed | Typical Solve Time | Play |
|---|---|---|---|
| Easy | Naked Single, Hidden Single | 5–10 min | Play Easy → |
| Medium | + Naked Pair, Hidden Pair, Pointing Pair | 10–20 min | Play Medium → |
| Hard | + Box-Line Reduction, Naked Triple, Hidden Triple | 20–40 min | Play Hard → |
| Expert | + X-Wing, Swordfish, XY-Wing, Coloring, Skyscraper | 30–60 min | Play Expert → |
| Evil | + Chains, Unique Rectangle, ALS, Finned X-Wing, Jellyfish, BUG | 45–90+ min | Play Evil → |
The “+” means all techniques from easier levels are also required. Always exhaust simpler techniques before applying harder ones.
Technique Count by Difficulty
| Skill Level | Techniques to Learn | Cumulative Total |
|---|---|---|
| Beginner | 2 | 2 |
| Intermediate | 4 | 6 |
| Advanced | 6–8 | 12–14 |
| Expert | 6–8 more | 18–22 |
You do not need to memorize every technique at once. Follow our technique progression guide for the recommended learning order, or use our solving checklist as a step-by-step companion while solving.
Bookmark or Print This Page
This cheat sheet is designed to be your puzzle-side companion. Keep it open in a second tab while solving, or print it and keep it next to your puzzle book. The decision tree in particular is valuable when you are stuck — following it step by step will eventually surface the technique you need.
For hands-on practice with any technique listed above, visit our practice page or learn page for interactive walkthroughs. Ready to test your skills? Jump into a puzzle at any difficulty:
- Easy — Singles only
- Medium — Singles + pairs
- Hard — Intermediate techniques
- Expert — Advanced techniques
- Evil — Everything on this cheat sheet
Frequently Asked Questions
What Sudoku techniques should I learn first?
Start with naked singles and hidden singles. These two basic techniques are enough to solve all easy puzzles and form the foundation for every other technique on this cheat sheet. Once singles feel automatic — meaning you spot them instantly without conscious effort — move to naked pairs and pointing pairs. These four techniques together will carry you through medium and most hard puzzles.
How many Sudoku techniques do I need to know?
It depends on the difficulty you want to solve. For easy puzzles, you only need two techniques (naked single and hidden single). For medium and hard, add four more for a total of six. For expert puzzles, you need roughly 12–14 techniques including fish patterns, wings, and coloring. For evil puzzles, the full set of 18–22 techniques becomes necessary. See the difficulty cheat sheet table above for the exact breakdown. Our technique progression guide provides the ideal learning order.
What technique do I use when I’m stuck?
Follow the decision tree above, starting from Step 1. The most common cause of being stuck is a missed basic technique or an error in pencil marks. Before trying anything advanced, re-verify your candidates (Step 3). In our experience, over 80% of “stuck” moments are resolved by finding a hidden single or a naked pair that was overlooked. If you have genuinely exhausted basic and intermediate techniques, move to X-Wing and coloring — they are the most frequently needed advanced techniques.
Is there a universal solving order for Sudoku?
Yes, and it matches the decision tree on this page. Always check basic techniques first (naked singles, then hidden singles), then intermediate (pairs, pointing pairs, box-line reduction), then advanced (fish patterns, wings, coloring), and finally expert techniques (chains, unique rectangles, ALS). Never jump to an advanced technique before exhausting simpler ones — simpler techniques are faster to check and more likely to fire. This order is universal across all valid Sudoku puzzles regardless of their difficulty rating.