Variant sudoku rules
Every constraint the library tags, in a sentence. Each rule has its own page with the full wording.
Cells
- Anti-Quadruples
- The digits in a circle at the corner of four cells must NOT appear in any of the cells touching it.
- Clock Faces
- The four digits around a marked corner increase in clockwise order, starting from one of the four cells.
- Counting Circles
- A digit in a circle indicates exactly how many circles in the entire grid contain that digit.
- Even
- Cells marked with a square contain even digits.
- Even/Odd
- Cells marked with a circle contain odd digits; cells marked with a square contain even digits.
- Fortress / Minimum
- A digit in a shaded (fortress) cell must be strictly smaller than all its orthogonal neighbours.
- Odd
- Cells marked with a circle contain odd digits.
- Odd/Even Lots
- Shaded regions must contain a specified count of odd digits and even digits.
- Quadruples
- The digits in the four cells surrounding a circle must include all of the digits listed in that circle.
- Star Battle
- Place one star in each row, column, and region. Stars have no value and may not touch each other, even diagonally.
- Sum Dots
- The number inside a diamond or dot is the sum of the digits in the cells it touches.
Grid
- Classic Sudoku
- Every row, column, and bold-outlined region contains each digit exactly once.
- Not 6x6
- This puzzle uses a digit set other than 1–6 (e.g. 5x5, 7x7, 9x9, or a non-standard digit range).
Edges and dots
- Consecutive
- Marked adjacent cells contain consecutive digits (may apply globally or be implied by other rules).
- Inequality
- Inequality markers (< or >) between adjacent cells point to the smaller digit.
- Kropki Black
- Digits separated by a black dot must be in a 1:2 ratio (one digit is exactly double the other).
- Kropki Pairs
- Digits separated by a white dot are consecutive; digits separated by a black dot are in a 1:2 ratio. Not all possible dots may be given.
- Nonconsecutive
- Orthogonally adjacent cells in the entire grid may not contain consecutive digits.
- Parity Diamonds
- A black diamond means the two cells it touches have the same odd/even parity; a white diamond means they have different parity.
- White Kropki
- Digits separated by a white dot must be consecutive (differ by 1).
- XV
- Digits separated by a V sum to 5; digits separated by an X sum to 10. Not all possible V and X clues are necessarily given.
Global rules
- Anti-King
- Cells that are a chess king's move apart (including diagonally adjacent) cannot contain the same digit.
- Anti-Knight
- Cells that are a chess knight's move apart (two steps in one direction, one step perpendicular) cannot contain the same digit.
- Anti-Queen
- Cells that are a chess queen's move apart (any direction, any distance) cannot contain the same digit.
- Diagonal
- Digits along the marked main diagonal(s) must not repeat (Sudoku-X).
- Disjoint
- Cells in the same relative position across different boxes must contain different digits.
- Doublers
- There are N cells in the grid (one per row, column, and region) where the digit counts as double its value for the purposes of cage sums or other totals.
- Dynamic Fog
- The grid is initially obscured by fog. Placing a correct digit clears the fog from that cell and its immediate neighbours.
- Fog of War
- The grid is initially covered in fog. Placing a correct digit reveals that cell and its adjacent cells.
- Loop
- Draw a one-cell-wide closed loop of orthogonally connected cells that never touches itself, not even diagonally.
- Mean Mini
- A subset of digits (e.g. 1–5) is used in the grid, exactly once per row and column, with no box constraints.
- Parity Mirror
- Cells reflected across the marked diagonal share the same parity: if one is odd, so is its mirror.
- Pole Position
- The first digit of each row gives the column holding that row's 1, and the first digit of each column gives the row holding that column's 1.
- Search Six
- A digit in an arrow cell indicates the distance to the 6 in that row or column.
- Snake
- Draw a one-cell-wide orthogonal path between two given endpoints that never touches itself, not even diagonally.
- Sudoku X
- Both main diagonals of the grid must also contain each digit exactly once.
- Yin Yang
- Shade some cells so that all shaded cells are orthogonally connected, all unshaded cells are orthogonally connected, and no 2x2 area is entirely shaded or entirely unshaded.
Lines
- Anti-Referenced Lines
- A line of length N must not contain the digit N anywhere along it.
- Arrows
- Digits on an arrow sum to the digit in that arrow's attached circle.
- Between Lines
- Digits along the line must be strictly between the digits in the circles at each end of the line.
- Chinese Whispers
- Adjacent digits on the line must have a difference of at least 2.
- Double Arrows
- The sum of digits on the line is equal to the sum of digits in the connected circles at each end.
- Dutch Whispers
- Adjacent digits on the line must have a difference of at least 4.
- Entropic Lines
- Any three consecutive digits along the line must form a full set of low (1–3), medium (4–6), and high (7–9) digits in any order.
- German Whispers
- Adjacent digits on the line must have a difference of at least 5.
- Greater Than Arrows
- Digits along an arrow strictly increase from the shaft towards the circle.
- Killer Lines
- Digits on the line do not repeat and sum to the clue attached to it.
- Lockout Lines
- Digits on a line must not be between the digits in the diamonds at each end, which must have a difference of at least 4.
- Modular Lines
- Any three consecutive digits along the line must belong to three different residue classes modulo 3 (i.e. one each from {1,4,7}, {2,5,8}, {3,6,9}).
- Nabner Lines
- No two digits along the line may be consecutive with each other.
- Palindrome Lines
- Digits along the gray line read the same forwards and backwards.
- Parity Lines
- Adjacent digits on the line must alternate between odd and even (opposite parity).
- Production Lines
- Each digit on the line is the sum of the two preceding digits on that line (Fibonacci-like sequence).
- Referenced Lines
- A line of length N must contain the digit N somewhere along it.
- Region Sum Lines
- For a blue region sum line, the sum of the digits on the line is the same within each region the line passes through.
- Renban Lines
- Digits on the purple line form a set of non-repeating consecutive digits, in any order.
- Sequence Lines
- Digits along a gray line form an arithmetic sequence with a constant difference between consecutive terms.
- Split Pea Lines
- Digits on a line between two circles sum to a two-digit number, whose tens digit is in one circle and whose ones digit is in the other.
- Sum Lines
- On each sum line, the shaded cells and the unshaded cells add up to the same total.
- Swans
- Each arrow line holds exactly one swan digit, which looks along the arrow and sees as many following cells as the line has arrowheads; those cells sum to the swan's value.
- Ten Lines
- Digits on each line must sum to 10.
- Thermometers
- Digits along a thermometer must strictly increase from the bulb end to the tip.
- Zipper Lines
- Digits at equal distances from the centre of the line must sum to the same total (the 'zipper sum'). Different zipper lines may have different sums.
Outside clues
- Indexing
- A digit in a specified column or row indicates the position of a particular digit in that row or column.
- Japanese Sums
- Clues outside the grid give the sums of contiguous groups of digits in that row or column, in order.
- Little Killer
- Clues outside the grid give the sum of digits along the indicated diagonal (digits may repeat on the diagonal unless otherwise stated).
- Numbered Rooms
- A clue outside the grid indicates the digit to be placed in the Nth cell from that direction, where N is the digit in the first cell.
- Remote Sums
- Clues outside the grid give the sum of digits at specified positions, not necessarily adjacent to the clue.
- Rossini
- An arrow outside a row or column indicates the direction in which the three nearest digits strictly increase. All possible arrows are given.
- Sandwich Sums
- Clues outside the grid give the sum of digits between the 1 and the 6 (or 1 and 9 in standard 9x9) in that row or column.
- Skyscrapers
- Each digit represents a skyscraper height. Taller buildings block shorter ones behind them. Clues outside the grid indicate how many skyscrapers are visible from that direction.
- Sweeper Clues
- A digit in a circle indicates how many odd digits are in its (up to 9) surrounding cells. A digit in a square indicates how many even digits surround it.
- Up-to-N Sums
- A clue outside a row or column gives the sum of the digits from the edge up to, but not including, the cell containing the digit N.
- X-Sums
- Clues outside the grid give the sum of the first X digits in that row or column, where X is the digit nearest the clue.
Regions
- Cage (Repeats Allowed)
- Cage digits sum to the clue; digits may repeat within the cage.
- Chaos Construction
- Regions are not given and must be determined by the solver according to the additional rules provided.
- Clones
- Shaded regions with the same shape must contain identical digits in the same positions.
- Extra Regions
- Shaded extra regions in the grid must also contain each digit exactly once.
- Irregular Regions
- Digits must appear once in each row, column, and bold-outlined irregular region (jigsaw).
- Killer Cages
- Digits in a dotted-outline cage must sum to the small number in the top-left corner and may not repeat.
- Look-and-Say Cages
- The clue in a cage is a look-and-say description of the digits inside. For example, '12' means one 2 inside the cage. Digits may repeat.