Sudoku Strategies: Every Technique in Order

Sudoku strategies form a ladder. Each rung is a pattern you can learn in a few minutes, and each one opens puzzles the previous rungs could not crack. This page lists all 38 sudoku solving techniques we use, from the singles every beginner knows to the forcing nets behind our hardest Killer puzzles, in the order a solver actually needs them. It is written for players who already finish Easy puzzles and want to know what to learn next.

Classic and Killer Sudoku share most of the ladder: 29 techniques apply to both, and 9 more are Killer sudoku techniques (cage techniques) that exist only in Killer. If you play only classic puzzles, skip the Killer entries; everything else applies to both.

How to use this ladder

Work from the top down. When you are stuck, the technique you need is almost always the simplest one you have not tried yet, not the fanciest one you know.

• Basic strategies (8 techniques) solve every Easy puzzle and most Medium ones. Master these before anything else.
• Tough strategies (15) are where Hard puzzles live and the advanced sudoku methods begin. Wings, fish and the core Killer cage logic.
• Diabolical strategies (7) are chain-based. They need pencil marks and patience, and they solve Expert puzzles.
• Extreme strategies (7) are what our Master and Legendary puzzles demand. Long chains, locked sets and forcing logic.
• Last resort (1) is educated trial and error. Legitimate, but it teaches you nothing, so it stays at the bottom.

The stall loop, in order:

  singles -> pairs / triples -> pointing pairs, box line reduction
          -> cage arithmetic (Killer only)
          -> wings and fish
          -> chains and colouring
          -> almost locked sets, forcing nets
          -> last resort

Drop back to the top after every placement.

Which technique does each level need?

Difficulty is the hardest step a puzzle forces, so each level starts where a new technique first becomes necessary. The bands below are the Sudoku Explainer (ER) bands used for every mode; the full story of how puzzles are rated is in sudoku difficulty levels.

Tiers and bands overlap a little. Simple Colouring and Naked and Hidden Quads sit in the tough tier, yet their ratings (quads 5.0 to 5.4, colouring 6.5 and up) land in the Expert band. The tier tells you how a technique feels; the number tells you which puzzles require it.

What the SE rating means

Every technique card in the ladder carries a rating chip. The number comes from Sudoku Explainer, the solver by Nicolas Juillerat: it always plays the easiest available step and rates a puzzle by the hardest step it had to take. A single value, such as 3.2 for X-Wing, is one rule. A range, such as 3.0 to 3.4 for pairs, covers several related rules (naked pair 3.0, hidden pair 3.4). A trailing plus, such as 6.6+ for XY-Chain, means the rating grows with the chain length.

Two markers need care:

• A star (*) marks a project rating. Sudoku Explainer has no rule for Killer cage logic, so we rate those techniques on our own ladder, placed between the Sudoku Explainer anchors. W-Wing carries one too, because the rater only finds it as a longer chain. Read starred numbers as "about this hard on the same scale", not as official Sudoku Explainer values.
• A dash (-) means unrated. Chute Remote Pairs, Empty Rectangle, 3D Medusa, Grouped X-Cycles, Finned X-Wing, Finned Swordfish, Almost Locked Sets and Death Blossom have no matching Sudoku Explainer rule, and we do not guess a number for them.

Classic vs Killer: what the cage techniques change

The nine Killer techniques are Innies and Outies, Cage Combinations, Captured Candidates, Cage Splitting, Multi-Cell Innies and Outies, Cage and Unit Overlap, Hard Killer Combinations, Rule of Parity and Cage Compare. Their project ratings run from 1.5 (cage combinations) to 4.0 (rule of parity), so they cover the same ground as the basic and tough tiers of classic play.

What changes in practice:

• Arithmetic replaces some pattern hunting. A cage with a known sum removes candidates that a classic grid could only remove with a wing or fish. Start with cage combinations and innies and outies, both in the ladder below.
• Givens disappear. Killer Expert, Master and Legendary puzzles on this site have no given digits at all. The cages alone must carry you, so the cage techniques are not optional extras at those levels.
• Classic patterns still work. X-Wing, Y-Wing and the chain techniques apply unchanged once the cage logic has trimmed the candidates.
• The top is higher. The hardest Killer puzzles we publish reach ER 12.8, against 11.1 for classic. See the hardest sudoku puzzles.

Reading the stall: which rung am I on?

When the grid stops moving, match what you see to the symptom, then try that rung.

If nothing on the list fits, go back to the top and look for a hidden single your last move created. That is the most common fix.

The full ladder

The ladder below lists all 38 techniques in complexity order, with their rating and difficulty tier. Filter to the mode you play, or read straight down: every article links to the next rung.

Where to practise

Every technique page ends with the difficulty level where the pattern first becomes necessary, so you can pick a matching puzzle and try it immediately. Start with easy Killer Sudoku for the cage basics, or hard classic Sudoku for wings and fish. If you are new to the order of play, the step-by-step solving guide walks through a full solve.