# Cryptic: Sudoku & 17 Variants

> Cryptic is a sudoku app with 17 variants, from Classic and Killer to Thermo and Miracle, plus a Technique Academy that teaches 25 solving techniques.

## Variants
- [Classic Sudoku](https://cryptic-sudoku.pages.dev/variants/classic/): The founding law, and the only one you need today.
- [Killer Sudoku](https://cryptic-sudoku.pages.dev/variants/killer/): Each dotted cage carries a sum.
- [Thermo Sudoku](https://cryptic-sudoku.pages.dev/variants/thermo/): Each thermometer runs from its bulb, the circle, to its tip.
- [Diagonal Sudoku](https://cryptic-sudoku.pages.dev/variants/diagonal/): Both main diagonals, corner to corner, must also hold each digit exactly once, just as a row or a column does.
- [Arrow Sudoku](https://cryptic-sudoku.pages.dev/variants/arrow/): Every arrow has a circle and a path.
- [Knight's Move Sudoku](https://cryptic-sudoku.pages.dev/variants/knight/): No two identical digits may sit a chess knight's move apart.
- [Sandwich Sudoku](https://cryptic-sudoku.pages.dev/variants/sandwich/): A clue outside the grid is a sum.
- [German Whisper](https://cryptic-sudoku.pages.dev/variants/german-whisper/): On a German Whisper line, any two neighbouring cells must differ by at least 5.
- [Renban Line](https://cryptic-sudoku.pages.dev/variants/renban/): The digits on a Renban line form a run of consecutive numbers, in any order you like.
- [Palindrome Line](https://cryptic-sudoku.pages.dev/variants/palindrome/): A palindrome line reads the same in both directions.
- [Between Lines](https://cryptic-sudoku.pages.dev/variants/between/): The digits on a between line must lie numerically between the two circled endpoints.
- [Region Sum Lines](https://cryptic-sudoku.pages.dev/variants/region-sum/): A region sum line is cut into segments wherever it crosses a box boundary, and every segment must add up to the same total.
- [Kropki Dots](https://cryptic-sudoku.pages.dev/variants/kropki/): A white dot between two cells means their digits are consecutive, differing by one.
- [XV Pairs](https://cryptic-sudoku.pages.dev/variants/xv/): A V between two cells means they sum to 5.
- [King's Move Sudoku](https://cryptic-sudoku.pages.dev/variants/king/): No two identical digits may sit a chess king's move apart.
- [Fog of War Sudoku](https://cryptic-sudoku.pages.dev/variants/fog-of-war/): The grid lies under fog.
- [Miracle Sudoku](https://cryptic-sudoku.pages.dev/variants/miracle/): Three rules at once, and every one is about pairs of cells.

## Techniques
- [Naked Single](https://cryptic-sudoku.pages.dev/techniques/naked-single/): A naked single is a cell with only one digit left that it could possibly hold.
- [Hidden Single](https://cryptic-sudoku.pages.dev/techniques/hidden-single/): A hidden single is a digit that has only one cell left to live in within a row, column or box.
- [Naked Pair](https://cryptic-sudoku.pages.dev/techniques/naked-pair/): A naked pair is two cells in one unit that share the same two candidates and nothing else.
- [Hidden Pair](https://cryptic-sudoku.pages.dev/techniques/hidden-pair/): A hidden pair is two digits that, within one unit, can only go in the same two cells.
- [Pointing](https://cryptic-sudoku.pages.dev/techniques/locked-candidates-pointing/): Pointing happens when a digit's remaining places in a box all lie along a single row or column.
- [Claiming](https://cryptic-sudoku.pages.dev/techniques/locked-candidates-claiming/): Claiming is the mirror image of pointing: a digit's places in a row or column all sit inside one box.
- [Naked Triple](https://cryptic-sudoku.pages.dev/techniques/naked-triple/): A naked triple is three cells in one unit whose candidates together draw from just three digits.
- [X-Wing](https://cryptic-sudoku.pages.dev/techniques/x-wing/): An X-Wing is a digit that appears in exactly two cells in each of two rows, with those cells sharing the same two columns.
- [Swordfish](https://cryptic-sudoku.pages.dev/techniques/swordfish/): A Swordfish is an X-Wing with a third arm: a digit confined to two or three cells in each of three rows, all within the same three columns.
- [XY-Wing](https://cryptic-sudoku.pages.dev/techniques/xy-wing/): An XY-Wing is three cells with two candidates each: a pivot holding X and Y, and two pincers, one holding X and Z and the other Y and Z, each seeing the pivot.
- [Hidden Triple](https://cryptic-sudoku.pages.dev/techniques/hidden-triple/): A hidden triple is three digits that, within one unit, can only go in the same three cells.
- [Naked Quad](https://cryptic-sudoku.pages.dev/techniques/naked-quad/): A naked quad is four cells in one unit whose candidates come from only four digits between them.
- [Hidden Quad](https://cryptic-sudoku.pages.dev/techniques/hidden-quad/): A hidden quad is four digits that, within one unit, can only go in the same four cells.
- [Skyscraper](https://cryptic-sudoku.pages.dev/techniques/skyscraper/): A Skyscraper is a digit with exactly two possible cells in each of two rows, where one cell from each row shares a column.
- [2-String Kite](https://cryptic-sudoku.pages.dev/techniques/2-string-kite/): A 2-String Kite links a row and a column that each hold a digit in only two cells.
- [Empty Rectangle](https://cryptic-sudoku.pages.dev/techniques/empty-rectangle/): An Empty Rectangle is a box where one digit's candidates lie only along a single row and a single column of that box, leaving an empty rectangle in the rest.
- [XYZ-Wing](https://cryptic-sudoku.pages.dev/techniques/xyz-wing/): An XYZ-Wing is a pivot cell holding three candidates, X, Y and Z, plus two pincers: one holding X and Z, the other Y and Z, each seeing the pivot.
- [W-Wing](https://cryptic-sudoku.pages.dev/techniques/w-wing/): A W-Wing is two cells that do not see each other but hold the same two candidates, X and Y, joined by a strong link on X: a unit where X has only two places, one seeing each cell.
- [Finned X-Wing](https://cryptic-sudoku.pages.dev/techniques/finned-x-wing/): A finned X-Wing is an X-Wing with a spare candidate, the fin, tucked beside one corner in the same box.
- [Jellyfish](https://cryptic-sudoku.pages.dev/techniques/jellyfish/): A Jellyfish is the fish family at its largest: a digit confined to the same four columns across four rows, with only two to four places in each row.
- [BUG+1](https://cryptic-sudoku.pages.dev/techniques/bug-plus-one/): BUG+1 arises when every unsolved cell has exactly two candidates except one cell that has three.
- [Unique Rectangle](https://cryptic-sudoku.pages.dev/techniques/unique-rectangle/): A Unique Rectangle is four cells in two rows, two columns and two boxes that could all hold the same pair of digits, which would let you swap them and get a second solution.
- [Simple Coloring](https://cryptic-sudoku.pages.dev/techniques/simple-coloring/): Simple Coloring follows one digit through a chain of cells linked in pairs, each pair being the only two places for that digit in some unit, and paints alternate cells in two colours.
- [XY-Chain](https://cryptic-sudoku.pages.dev/techniques/xy-chain/): An XY-Chain is a run of two-candidate cells in which each neighbour shares a digit with the next, the chain starting and ending on the same digit.
- [X-Chain](https://cryptic-sudoku.pages.dev/techniques/x-chain/): An X-Chain follows one digit along a chain of cells linked alternately by strong links, units where the digit has only two places, and weak links, where it merely cannot be in both.

## More
- [FAQ](https://cryptic-sudoku.pages.dev/faq/)
- [Full text of this site](https://cryptic-sudoku.pages.dev/llms-full.txt)