Everything you need to know about Shikaku and PlayShikaku.com.
The Game
Shikaku is a Japanese logic puzzle where you partition a rectangular grid into non-overlapping rectangles. Each rectangle must contain exactly one number, and the rectangle's area must equal that number. For example, a rectangle containing the number 6 must have exactly 6 cells (which could be 1×6, 6×1, 2×3, or 3×2).
Every Shikaku puzzle has a unique solution reachable by pure logical deduction — no guessing is required.
Shikaku was invented by Nikoli, the Japanese puzzle company that also popularized Sudoku. The name means "divide by box" (四角に切れ) in Japanese. It was first published in 1989 and has appeared in puzzle books and magazines worldwide ever since.
Both are logic puzzles from Nikoli, but they're quite different in structure. Sudoku is about placing digits with no-repeat constraints in rows, columns, and boxes. Shikaku is about spatial partitioning — covering a grid with rectangles of specific areas. Shikaku has simpler rules and a more visual, geometric feel. Many players find it more approachable as a first logic puzzle, while the hardest difficulties rival Sudoku in depth.
Yes. Every puzzle on PlayShikaku.com is verified by a solver before being served to you. The solver confirms there is exactly one valid arrangement of rectangles. If a generated puzzle has zero solutions or more than one, it is discarded and a new one is generated.
No. All puzzles on this site are solvable by pure logic. That said, on extreme and nightmare difficulty puzzles, the logical chains can be very long and require advanced techniques like hypothesis testing (assuming a placement and checking for contradictions). That's still logic — just more demanding logic.
Playing the Game
Click (or tap on mobile) and drag across the grid. A dashed outline shows your current selection as you drag. When the outline is green, the placement is valid — release to place it. When the outline is red, the placement is invalid (wrong area, contains two clues, or overlaps an existing rectangle), and releasing will do nothing.
Click on the rectangle to select it (it will show a highlight border), then press Delete or Backspace on your keyboard, or click the Delete button in the toolbar below the grid.
Yes. Press Ctrl+Z to undo and Ctrl+Y to redo. The undo and redo buttons in the toolbar do the same thing. There's no limit on undos and no penalty for using them.
Partially. Keyboard shortcuts for undo (Ctrl+Z), redo (Ctrl+Y), delete (Delete/Backspace), and cancel (Escape) are all supported. Full keyboard-only grid navigation (arrow keys to move, enter to draw) is on the roadmap.
Click the Hint button in the toolbar. The game will reveal one correct rectangle placement from the solution. Hints are counted and displayed in your puzzle completion stats. There's no limit on hints — use them freely while learning, and challenge yourself to reduce your hint count as you improve.
Progress and Data
Yes. Your current puzzle state is automatically saved to your browser's localStorage as you play. When you return to the site — even days later — your puzzle is restored exactly where you left off.
Best solve times are stored locally in your browser via localStorage. They are not synced to any server. If you clear your browser data or switch to a different device, your times will not carry over.
No. There are no accounts, no registration, and no login required. The game works entirely in your browser. We don't know who you are, and we don't need to.
Yes. PlayShikaku.com is designed to work on all screen sizes. Touch controls are fully supported — drag to draw, tap to select, tap the toolbar for actions. The game can also be added to your home screen as a PWA (progressive web app) for a more native-feeling experience.
Pricing and Unlock
Yes. 40 puzzles are permanently free: 10 each at Easy, Medium, Hard, and Extreme. You can play indefinitely without paying anything. Ads are shown to free users to support the site.
It's a one-time payment — no subscription, no recurring charges.
When you purchase, you receive a license key. Enter the key in the "Unlock Shikaku" dialog (accessible from the toolbar) on any device to activate the unlock on that browser. The key can be used on multiple devices.
Check your email for the purchase receipt from Stripe, which includes your license key. If you can't find it, reach out via Ko-fi with your purchase details and we'll help you recover it.