In the game Shikaku, the goal is to draw rectangular borders around cells of the size equal to a circled number enclosed (see Rules tab). To play, use the mouse or arrow keys to draw the borders, or rooms:

• You can begin to draw a rectangle from any cell. With the mouse, left-click and hold to begin the rectangle, then drag the mouse in the shape desired. For instance, if you want a 2-high 3-wide rectangle over a cell with a '6' in it, click on the cell describing the upper left of the rectangle, then move the mouse two cells to the right and down 1 to make the 2x3 rectangle. While the mouse is down you can change the shape as desired.
• A right-click within a room removes any prior borders and starts anew. The drawing tool will not allow you to create a room that conflicts with an existing room.
• In alternate to the mouse drag, you can do the same by moving around the board with the arrow keys, then pressing the shift button to start a rectangle shape, expanding it in any direction with the arrow keys.
• Pressing the backspace on a cell within a defined room clears its existing rectangle. It may not always be obvious that a room has been cleared if other rooms' borders coincide with the borders of the deleted room. (Assist mode below can help visualize drawn rooms.)

In Assist Mode (0), the default, only the existance of errors or incomplete numbers is indicated. In Assist Mode (1), the number of errors and incomplete numbers is indicated, see game rules. In Assist Mode (2) completed rooms are colored green if they are of the correct size compared to the enclosed number. Rooms with errors are colored red, for instance if they contain two numbers, no numbers, or are of the wrong size for the enclosed number. Note a green room is not by definition the correct final solution, only that it is created with the correct constraints. In some cases the solve difficulty will greatly decrease in Assist Mode (1) or higher, so select depending upon the level of challenge desired. The game border will turn green if the grid is completed without error. You can click the "undo" button on the bottom of the page to undo previous moves.

Below, enter puzzle code (0-0) for one of a list of pre-defined puzzles, or a puzzle descriptor (see "Puzzles" tab). Puzzle code 0 shows an example completed puzzle that can be helpful. The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

Shikaku (四角に切れ Shikaku ni Kire; or "Divide By Box") is a logic puzzle published by Nikoli. In Shikaku, the board begins with many cells containing numbers in black circles. These numbers indicate the size of a rectangular "room" that must be drawn around it. The full set of rules below relate to those numbers and how to complete the puzzle.

1. All numbered cells must be contained within a drawn rectangular room containing the same number of cells as the number.
2. No room can contain two numbers, nor no numbers.

Puzzles can be invoked by either a numerical entry from 0-0, or through a character description of the puzzle itself, entered into the Display form on the 'Game Play' tab. The numbered puzzles are hand-crafted of varying difficulty, roughly easy to hard. Puzzle 0 shows a completed correct puzzle.

To describe a puzzle, the character string must be of the form: "WxH:<digit-descriptor>", where W is a number indicating the width of the grid, and H the height. The digit descriptor is a list of the pre-defined numbered cells, from left to right, then top to bottom. Blank cells are represented with a '-' character. To assist in the definition of a sparse board, a combination of b consecutive blanks can be represented with a lowercase letter from 'a' to 'z', corresponding to 1 to 26 consecutive blanks. Number values greater than '9' should be represented with capital letters 'A' to 'Z' representing 10 to 35. A dot '.' can be used as a visual separator, for example between rows. An example descriptor is as follows for entry 1: 'descr'.

For Shikaku there are 1 demo puzzles that can be helpful to walk through solving methods. They are puzzle codes []. Enter them in the Game Play tab with the code number and there will be added a demo panel to help with the solve.

This playground was written using javascript and is available open source. All code is checked into the github repo at ohmec/puzzles. Feel free to file bugs there!