1. Start here
New to Shikaku? These two pages are all you need to play.
2. Solving techniques
Each technique has its own deep guide with real examples generated by our solver. Start with the strategy overview.
Prime numbers
Why 2, 3, 5, 7… are always straight strips.
Corners and edges
How the border cuts a number’s options.
Forced rectangles
Spot numbers with only one rectangle left.
Unreachable cells
Cells only one number can reach.
The overlap technique
Claim cells every option shares.
Region counting
Use area totals of sealed-off regions.
Contradiction
The last-resort technique for hard grids.
Worked example
A full 7×7 solve, step by step.
3. Beyond the grid
The maths, the teaching ideas, the design craft and the computer science.
4. Context
Where Shikaku came from and how it compares with similar puzzles.