Single
Finds a cell whose digit, or a digit whose place, is already decided.
5 techniques
Techniques
The techniques this site's puzzles actually use. Every one of them is shown on a real board.
155 techniques
Complex Single
Uses the candidates a placement has just removed to find the next placement.
3 techniques
Locked Candidates
Candidates confined to a line-box crossing are removed from the rest of the line or box.
3 techniques
Subset
A set of cells holding exactly as many digits, which then belong to nobody else.
10 techniques
Fish
A digit that lines up in equally many rows and columns is removed where they do not meet.
8 techniques
Single Digit Pattern
Strong and weak links alternate along a chain, and its ends force a conclusion.
5 techniques
Wing
Branches through cells with few candidates, ruling out candidates incompatible with every branch.
4 techniques
Irregular Wing
Branches through cells with few candidates, ruling out candidates incompatible with every branch.
9 techniques
Almost Locked Candidates
Pairs an almost-locked set with an almost-hidden set across two houses, and removes what they cannot share.
2 techniques
Avoidable Rectangle
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
8 techniques
Unique Loop
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
3 techniques
Unique Rectangle
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
24 techniques
- Unique Rectangle 2B/1Medium
- Unique Rectangle 2D/1Medium
- Unique Rectangle Type 1Medium
- Unique Rectangle Type 4Medium
- Hidden Unique RectangleMedium
- Unique Rectangle 3N/2Medium
- Unique Rectangle 3U/2Medium
- Unique Rectangle 3X/2Medium
- Unique Rectangle 4C/3Medium
- Unique Rectangle Burred SubsetMedium
- Unique Rectangle Type 2Medium
- Unique Rectangle Type 6Medium
- Unique Rectangle External Type 2Hard
- Unique Rectangle Type 3Medium
- Unique Rectangle 4X/1LMedium
- Unique Rectangle 4X/1UMedium
- Unique Rectangle External Turbot FishHard
- Unique Rectangle 4X/2LMedium
- Unique Rectangle External XY-WingHard
- Unique Rectangle Sue de CoqHard
- Unique Rectangle 2DMedium
- Unique Rectangle 3XMedium
- Unique Rectangle Singly Linked ALS-XZHard
- Unique Rectangle Doubly Linked Almost Locked Sets XZHard
Empty Rectangle
Candidates confined to a line-box crossing are removed from the rest of the line or box.
1 techniques
Extended Rectangle
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
2 techniques
XYZ-Ring
Candidates that close into a loop rule out what lies inside or outside it.
4 techniques
Sue de Coq
Fills a line-box overlap with two candidate sets, and removes those candidates outside the sets.
2 techniques
Complex Fish
Uses equal-sized groups of rows, columns, or boxes where one digit appears only across the other group.
17 techniques
- Finned Franken SwordfishHard
- Siamese Finned Franken SwordfishHard
- Sashimi Franken SwordfishHard
- Finned Mutant SwordfishHard
- Siamese Sashimi Mutant SwordfishHard
- Finned Franken JellyfishHard
- Sashimi Franken JellyfishHard
- Siamese Sashimi Franken JellyfishHard
- Siamese Sashimi Mutant JellyfishHard
- Siamese Sashimi Franken SquirmbagExpert
- Siamese Finned Mutant SquirmbagExpert
- Sashimi Mutant SquirmbagExpert
- Siamese Sashimi Mutant SquirmbagExpert
- Siamese Finned Franken WhaleExpert
- Finned Mutant WhaleExpert
- Sashimi Mutant WhaleExpert
- Siamese Sashimi Franken LeviathanExpert
Borescoper Deadly Pattern
Assumes a pattern that would break the single solution, and prevents it.
1 techniques
Extended Subset Principle
A set of cells holding exactly as many digits, which then belong to nobody else.
1 techniques
BUG
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
3 techniques
Broken Wing
Places a candidate, finds the contradiction it causes, and removes it.
1 techniques
ER Intersection Pair
A group holding one more digit than it has cells, related to another such group.
1 techniques
Firework
Combines the constraints of a larger arrangement to narrow the candidates.
1 techniques
AIC and chains
Strong and weak links alternate along a chain, and its ends force a conclusion.
16 techniques
- Purple CowHard
- X-ChainHard
- Alternating Inference Chain (AIC)Hard
- Continuous Nice LoopHard
- Discontinuous Nice LoopHard
- XY-ChainHard
- XY-X-ChainHard
- Grouped Purple CowHard
- Finned ChainHard
- Finned Grouped ChainHard
- Grouped Alternating Inference Chain (Grouped AIC)Hard
- Grouped Continuous Nice LoopHard
- Grouped Discontinuous Nice LoopHard
- Node CollisionHard
- Grouped Self-ConstraintHard
- Grouped XY-ChainHard
ALS chains
A group holding one more digit than it has cells, related to another such group.
5 techniques
Reverse BUG
Because the puzzle has exactly one solution, any pattern that would give two can be ruled out.
2 techniques
Trivalue Oddagon
Places a candidate, finds the contradiction it causes, and removes it.
1 techniques
Symmetry
Uses the symmetry of the givens and the pairing of digits it implies.
1 techniques
Aligned Exclusion
Places a candidate, finds the contradiction it causes, and removes it.
3 techniques
Forcing Chains
Follows every branch of a choice and keeps what they all agree on.
7 techniques
Domino Loop
Candidates that close into a loop rule out what lies inside or outside it.
1 techniques
Multi-sector Locked Set
Counts candidates across overlapping regions and removes what cannot fit.
1 techniques