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Sudoku techniques are repeatable logical deductions that let you place a digit or eliminate a candidate without an unsupported guess.
You do not need to memorize every named pattern before you can solve well. Most puzzles are solved by repeatedly using the simplest logic that the current grid supports, then returning to easier deductions after each placement or elimination.
A useful high-level progression is:
direct placements → intersections → subsets → single-digit patterns and Fish → Wings → Coloring and Chains → uniqueness and expert structures
This page is the map of the VeyraPlay Sudoku technique library. It explains what each family is for, how the families relate, and where to go when you want the full proof for one technique.
What counts as a Sudoku technique?
A technique is a proof pattern. It tells you why a digit must be placed or why a candidate can be removed.
That is different from a search method.
For example:
- scanning tells you how to inspect the grid systematically;
- crosshatching tells you how to focus on one digit across a box and its crossing lines;
- Hidden Single is the deduction you may discover when that scan proves the digit has only one possible position in a house.
The distinction is useful because good solving has two parts:
- recognition — finding a promising structure;
- proof — applying a valid deduction to that structure.
The Guides below cover both, but named techniques are defined by the proof, not by how your eyes happened to find it.
Placements and eliminations
Almost every human-style Sudoku step produces one of two kinds of progress.
Direct placements
You prove the value of a cell and write the digit into the grid.
Singles are the clearest examples. If a house has one empty cell, if a cell has one legal candidate, or if a digit has one possible position in a house, the placement is forced.
Candidate eliminations
You prove that a digit cannot occupy a particular unsolved cell.
Locked Candidates, subsets, Fish, Wings, Coloring, and Chains often work this way. An elimination may not fill a cell immediately, but it can create a Single or simpler pattern on the next pass.
This is why advanced solving still depends heavily on beginner logic: a sophisticated elimination is often valuable because it unlocks a simple placement.
Foundations
These are search skills rather than isolated proof patterns, but they are the practical foundation of the technique library.
Scanning
A systematic way to search rows, columns, boxes, cells, or one digit for constrained positions.
Use scanning to find last missing digits, Singles, and later candidate restrictions without staring randomly at all 81 cells.
Crosshatching
Use existing copies of one digit in crossing rows and columns to restrict that digit inside a box.
When only one position survives, crosshatching has revealed a Hidden Single. If two positions survive on one line, the same observation may later support Locked Candidates.
Singles
Singles are the basic forced-placement family.
The simplest case is a Full House / last missing digit: one house has only one empty cell, so the missing digit must go there.
The two dedicated Singles Guides below cover the other fundamental viewpoints.
Naked Single
One cell has exactly one remaining legal candidate.
The proof is cell-first:
What can go in this cell?
Only one digit.
Hidden Single
One digit has exactly one remaining legal position in a row, column, or box.
The proof is digit-first inside one house:
Where can this digit go in this house?
Only one cell.
Intersections
Intersection techniques use the overlap between a box and a row or column.
The digit is not necessarily placeable yet. Instead, its allowed positions become confined strongly enough that candidates can be removed elsewhere.
Locked Candidates
A digit is confined to the overlap between a box and a row or column.
This is the family-level idea behind Pointing and Claiming.
Pointing Pairs / Pointing Candidates
Start from a box. If all candidates for one digit inside that box lie on the same row or column, remove that digit from the rest of the shared line outside the box.
Box-Line Reduction / Claiming
Start from a row or column. If all candidates for one digit on that line lie inside one box, remove that digit from the rest of that box.
Subsets
Subsets reserve N digits for N cells inside one house.
That reservation means those digits cannot appear in other cells of the same house, or that other candidates can be removed from the reserved cells, depending on whether the subset is naked or hidden.
Naked Pair
Two cells reserve two digits.
Hidden Pair
Two digits are restricted to two cells.
Naked Triple
Three cells contain only three digits between them.
Hidden Triple
Three digits are restricted to three cells.
The same logic extends to Naked Quad and Hidden Quad. The Sudoku Subsets guide connects all six named subset pages through the general N cells ↔ N digits model.
Fish
Fish track one candidate digit across several rows and columns.
A Fish uses a set of base houses and a matching set of cover houses. When the candidate is restricted to the required pattern, matching candidates outside the base structure can be eliminated from the cover houses.
X-Wing
Two base sets restrict the digit to two cover sets.
Swordfish
Three base sets restrict the digit to three cover sets.
The family continues with Jellyfish and Finned X-Wing, while the Sudoku Fish guide explains the base-set/cover-set model shared across basic and finned forms. Sashimi X-Wing is covered inside the Finned X-Wing guide rather than split into a competing URL.
Wings
Wings use small candidate sets and peer relationships to prove that at least one of several linked cells must contain a shared candidate.
That shared consequence allows eliminations from cells that see the relevant endpoints.
XY-Wing
A bivalue pivot connects two pincers and forces the shared Z candidate into one of them.
XYZ-Wing
A three-candidate pivot changes the common-peer requirement for the Z elimination.
W-Wing
Two matching bivalue cells are connected through a Strong Link.
WXYZ-Wing
Four cells contain four candidates under a restricted shared-candidate relationship. It is a useful bridge from named Wings into Almost Locked Set reasoning.
For the family-level comparison between XY-, XYZ-, W-, and WXYZ-Wing, use Sudoku Wings.
Single-digit Strong-Link patterns
These patterns follow one candidate digit through short Strong-Link structures.
They are often easier to recognise than a general Chain because the shape is compact and the target candidate stays the same throughout the proof.
Skyscraper
Two conjugate pairs share one aligned side and force one of two roof candidates.
Two-String Kite
One row Strong Link and one column Strong Link connect through a box.
Empty Rectangle and Turbot Fish extend this single-digit branch. Turbot Fish is best understood as a short X-Chain rather than as a base-set/cover-set Fish despite its historical name.
Links, Coloring, and Chains
Once individual patterns stop being enough, it becomes useful to reason about candidate implications.
Strong and Weak Links are the vocabulary. Coloring and Chains are ways to organise those implications across a larger part of the grid.
Strong Links
A Strong Link says that if one candidate is false, the other must be true within the relevant relationship.
Weak Links
A Weak Link says that if one candidate is true, the other must be false.
Sudoku Chains
Chains connect alternating implications so that a conclusion can be proved beyond one local pattern.
Simple Coloring
Use two states across a conjugate-pair network for one candidate digit.
X-Chain
Follow one candidate digit through alternating links.
XY-Chain
Follow candidate implications through a chain of bivalue cells.
The expert implication branch continues through Alternating Inference Chains, X-Cycles, Grouped AIC, Multi Coloring, and 3D Medusa. Remote Pair provides another compact chain pattern. Beyond those, Almost Locked Sets, ALS-XZ, and Forcing Chains extend the same logical vocabulary into expert structures.
Uniqueness
Uniqueness techniques use the fact that a properly constructed puzzle has one intended solution to rule out certain candidate structures.
They require more care than ordinary constraint deductions because the proof depends on verified uniqueness, not just the three row/column/box constraints.
Unique Rectangle
Avoid a local two-solution deadly pattern when the puzzle is verified to have one solution.
The Sudoku Uniqueness Techniques guide maps Unique Rectangle Types 1–6, Hidden Rectangle, Avoidable Rectangle, BUG, and BUG+1. V2 keeps most UR subtypes inside that family architecture rather than creating a separate URL for every type.
Recommended learning order
For a first complete path through the current library:
Scanning and Crosshatching
↓
Full House / Naked Single / Hidden Single
↓
Candidates
↓
Locked Candidates
↓
Pairs
↓
Triples
↓
X-Wing and Swordfish
↓
Wings and short single-digit patterns
↓
Strong / Weak Links
↓
Coloring and Chains
↓
Uniqueness → ALS / advanced Chains / ForcingThis is a curriculum order, not a universal ranking of difficulty.
You should also keep returning to earlier techniques. If a Swordfish removes one candidate and creates a Hidden Single, the next correct move is the Hidden Single — not another Swordfish search.
Technique difficulty is approximate
A named technique does not have one fixed human difficulty in every puzzle.
Recognition can change dramatically depending on:
- candidate density;
- whether notes are visible or automatic;
- how many distracting structures are present;
- whether the pattern is clean or irregular;
- how much simpler logic had to happen before the pattern appeared;
- the solver's familiarity with that family.
This is why two puzzles containing the same highest-level technique can still feel very different.
Puzzle difficulty should come from the actual human-style solving path, not from this library order alone.
How do you know which technique to look for?
Do not search every technique name in sequence. First ask what kind of structure the grid is showing.
- One house is almost complete → look for a last missing digit.
- One cell is highly constrained → look for a Naked Single.
- One digit has very few positions in a house → look for a Hidden Single or intersection restriction.
- A few cells share a small candidate set → inspect subsets.
- One digit forms sparse repeated positions across rows/columns → inspect single-digit patterns or Fish.
- Several bivalue cells interact → inspect Wings or XY-style Chains.
- Strong-Link networks appear → inspect Coloring and Chains.
- A rectangle threatens two interchangeable solutions → inspect uniqueness logic only if uniqueness is verified.
The general strategy is to choose the simplest family supported by the visible structure.
How to use the technique library
If you are learning a technique:
- understand the condition that must be true;
- inspect a validated example;
- identify exactly which placement or elimination is proved;
- explain the proof in your own words;
- practise recognition separately from execution;
- mix the technique with earlier logic only after the proof feels reliable.
If you are stuck in a live puzzle:
- return to Singles and recent changes first;
- identify whether the remaining structure is cell-first, digit-first, subset-based, single-digit, bivalue, link-based, or uniqueness-based;
- open the relevant family rather than a random advanced page;
- prove the deduction against your actual candidates;
- return to simpler logic immediately after progress.
Technique names are not perfectly universal
Sudoku communities and solving programs sometimes group, split, or name patterns differently.
For example, one source may treat a named shape as a special case of a broader Chain; another may teach it as its own recognisable technique. Terms such as house, unit, conjugate pair, Strong Link, Pointing, or Claiming can also vary slightly in presentation.
VeyraPlay uses one consistent internal vocabulary while noting common aliases where they help a reader recognise material from other sources.
FAQ
How many Sudoku techniques are there?
There is no single final count. Basic families are widely shared, but advanced solving systems differ in how they name, group, or generalise patterns.
Which Sudoku technique should I learn first?
Start with direct placements: last missing digits, Naked Singles, and Hidden Singles. Scanning and crosshatching help you find those deductions reliably.
Do I need advanced techniques for Easy Sudoku?
Normally not in a well-calibrated difficulty system. Easy puzzles should be dominated by direct placements and simple candidate logic.
Is X-Wing harder than a Hidden Triple?
Often, but not universally. Recognition difficulty depends on the specific grid, candidate state, interface, and solver experience.
Do advanced techniques replace beginner techniques?
No. Advanced techniques usually create new candidate information, after which you should re-scan for Singles and simpler deductions again.
Explore strategy as well as technique
Knowing how a pattern works is only half the job. Sudoku Strategies explains how to organise your search, when to change viewpoint, and which family to inspect next.