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Sudoku Rules and Strategies

Sudoku is a logic puzzle with simple rules. Whether you are solving your first grid or refining your technique, these rules and strategies will help you progress.

Core Sudoku strategies

Every Sudoku can be solved by pure logic. Here are the basic strategies Sudoked.com uses in its hints.

A 9 tile being placed into the only empty cell of the central Sudoku box

Basics

The essential Sudoku rules and the first solving methods every player should know before moving on to candidate-based techniques.

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Sudoku grid with a blue number tile being placed into the final cell

Foundations

Two foundational exclusion deductions — one candidate left in a cell or one position left for a digit — plus Pointing and Claiming, the two directions of one box–line reduction rule.

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Three Sudoku cells locking candidates 1, 2 and 3 into one row

Locked Subsets

Locked subsets: N cells sharing N candidates (naked) or N digits sharing N positions (hidden) inside one house — pairs, triples and quadruples.

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A basic fish construction balancing one digit across base and cover houses

Fish

The basic fish family: X-Wing, Swordfish and Jellyfish balance one digit across N base houses and N cover houses.

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Three strong links of one digit closing into a ring

AIC Chains

Open alternating inference chains (AICs): exhaustive alternatives joined as strong-inference nodes, with consecutive nodes connected by weak inferences. This group covers same-digit X-Chains and bivalue-cell XY-Chains.

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An alternating Sudoku candidate ring leading to an elimination

AIC Rings

Closed alternating inference chains: same-digit, bivalue, and mixed rings whose closing weak inference is verified independently of the path.

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Two almost locked sets linked by candidate 1 eliminate candidate 3 from a shared peer

ALS-XZ Wings

Almost-locked-set constructions linked by restricted common candidates: XY-Wing through TUVWXYZ-Wing, plus the doubly linked ring forms.

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Four candidate cells forming a unique rectangle with one extra candidate

Uniqueness

Conditional eliminations that use an explicitly stated unique-solution premise: Unique Rectangles, Unique Loops and the Bivalue Universal Grave (BUG).

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Every candidate of one Sudoku cell branching to the same forced conclusion

Forcing Fallback

Exhaustive forcing: every alternative of a source cell or house is tested and only conclusions shared by all branches are kept.

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A detailed reference to 57 Sudoku solving techniques

Sudoked.com organizes its English technique guides around the modern mathematical families: locked and almost locked sets, fish, and alternating inference chains (AICs). Uniqueness and exhaustive forcing deductions state their additional assumptions separately. Familiar historical names remain as searchable aliases, while each guide defines the actual cells, candidate sets, houses, links, and visibility conditions that make the deduction valid.

Each guide uses a concrete Sudoku position and a candidate-by-candidate proof. The text identifies the operands first, then states the exact placement or elimination and why it follows. Annotated screenshots illustrate those relations but do not define them by shape. The guides document page-level technique concepts; the live hint engine and its generated explanations are maintained and tested separately.

The technique names, groupings and definitions in these guides were aligned with the modern ALS–fish–AIC framework maintained by strmckr (GitHub) in the r/sudoku wiki, rather than the legacy descriptions that still circulate online.

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Every page on Sudoked.com is sudoku no ads — the rules page, the game and statistics. No trackers, no promoted content, no interruptions. Just the puzzle and the logic.