Shikaku Puzzle Generator
Every number in the grid is the area of the rectangle that contains it, and every cell belongs to exactly one rectangle. That is the whole rule, and it makes for a puzzle about factor pairs and fit: a 6 can be 1×6, 2×3, 3×2 or 6×1, and which one it is depends entirely on what its neighbours need. Each grid here is built by cutting a solution first and then proved to have no second answer.
What this generator does
Cuts the grid into rectangles of up to six cells, puts each rectangle's area into one of its own cells as the clue, and then solves the clues from scratch. Anything with a second solution is rejected and another cut tried.
How to use this tool
- Choose the grid size.
- Divide the grid into rectangles, each containing exactly one number.
- Make each rectangle's area equal to the number inside it.
- Reveal the answer to check, or seed the grid to reissue it.
Understanding the controls
- Grid size
- Between 4 and 10. The solver is comfortable well past ten; the limit is where the grid stops being pleasant to solve by hand.
- Seed
- Reproduces the same cut and the same clues, so a puzzle can be printed twice identically.
- Show the answer
- Shades alternate rectangles so the cut is visible at a glance.
Common use cases
- Factor practice disguised as a puzzle
- A spatial reasoning exercise that needs no arithmetic beyond multiplication
- Printable puzzles where the answer is known and provably unique
- A gentler alternative to Sudoku for younger solvers
- Testing a rectangle-partition solver against verified instances
How this generator works
The solver always attacks the first uncovered cell, trying every rectangle that could contain it: each unused clue, each factor pair of that clue's value, each position that covers both the clue and the cell without swallowing a second clue. That ordering is what keeps the search small enough to prove uniqueness in under a millisecond even at ten by ten.
Randomness and fairness
The cut and which cell in each rectangle carries the clue are random; the single answer is proved. Seeded puzzles reproduce exactly and are therefore explicitly not cryptographically secure, and unseeded ones use the browser's cryptographically secure generator.
For how randomness is produced across the whole site, see how Generate Random works.
Limitations and good to know
- Rectangles hold at most six cells, so the long thin shapes some published puzzles use are rare.
- The grid is square. Rectangular boards are common in print and are not offered here.
- Difficulty is not graded, and a unique answer says nothing about how hard it is to find.
- The answer is shown by shading alternate rectangles rather than by drawing their borders.
- Puzzles are not kept between visits; seed one you want again.
Privacy and your data
The cut and the clues are generated in your browser and solved there. Nothing is transmitted or stored.
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