How to Play

The rules

Fill every white cell with a digit from 1 to 9.
The number in the top-left triangle of a dark cell is a down clue — the digits below it must sum to that value.
The number in the bottom-right triangle is an across clue — the digits to its right must sum to that value.
No digit may appear more than once within a single run (consecutive white cells in the same row or column).

Controls

Click a white cell to select it, then tap a number on the pad or press 1–9 on your keyboard.
Press Delete or Backspace (or click Erase) to clear a cell.
Use arrow keys to navigate between white cells.
Cells highlighted in red violate a run — either a repeated digit or a sum that exceeds the clue.

History of Kakuro

Kakuro traces its roots to the United States, where it first appeared as "Cross Sums" in Dell Magazines in 1966. For decades it remained a niche American puzzle, tucked alongside crosswords and word games.

In 1980, Japanese publisher Nikoli discovered Cross Sums, adapted it for Japanese readers, and published it under the name 加算クロス (Kasan Kurosu) — "addition cross". The name was later shortened to Kakuro (加クロ), a contraction of kasan (addition) and kurosu (cross).

Nikoli refined the puzzle's aesthetics — insisting on rotationally symmetric grids and a clean presentation — and Kakuro became enormously popular in Japan through the 1990s.

Like Sudoku, Kakuro arrived in the English-speaking world in 2005 when The Times (London) began publishing it. Puzzle books followed quickly, and within a year Kakuro was appearing in newspapers worldwide as "the next Sudoku".

Tips & Fun Facts

Solving strategies

Start with runs that have only one valid combination — e.g., a 2-cell run summing to 3 can only be {1, 2}; summing to 17 can only be {8, 9}.
A 3-cell run summing to 6 must be {1, 2, 3}; summing to 23 must be {6, 8, 9}.
Where two runs cross at the same cell, use the constraints of both to narrow candidates.
If a run's only valid combination contains a digit that must appear, note it as a definite placement.
Build a mental or written list of possible digit sets for short runs — this is the Kakuro equivalent of naked singles in Sudoku.

Did you know?

A valid Kakuro puzzle always has exactly one solution — though finding it may take considerable reasoning.
Unlike Sudoku, Kakuro requires arithmetic: you must track running sums, not just digits.
The maximum possible sum for a run of n cells is (9 + 8 + … + (10−n)).
Kakuro puzzles can range from tiny 4×4 grids to enormous 20×20 constructions used in competitions.

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