In Slitherlink, the goal is to draw one continuous line along the borders between cells (see Rules tab). To create the borders you can use the mouse or keyboard buttons:

• A left-click on the space between cells creates a border line between vertices, while a right-click removes an existing border line.
• You can drag around to continue to draw the border line, or erase an existing line.
• Alternately, once on a cell boundary, you can press the shift key and then the arrow keys to add more borders in the direction of arrow keys.
• Additionally, once the cursor is on a border, you can press the space bar to toggle the border state, or press '1' to set, or '0' or backspace to clear.
• You can use the mouse to middle-click on a line to add an '×' in a line space, indicating that it is marked as disabled, i.e. determined by the user to not be able to contain a line. Similarly you can press the X key while the cursor is on a border to set as disabled.
• To help visualize the growing shape, you can left-click on a cell to toggle its color between the default white, and gray. This has no influence on the solving of the puzzle, but can help visualize the cells in between the lines of the full final loop (see rules). Once clicked, you can drag the mouse to add to the gray coloration. A right-click on a cell clears it back to white, and a right-click drag can clear multiple cells at once.
• With the arrow keys you can move around the board and press '1' to set a cell gray, or '0' or backspace to return to white. Once on a cell of either color, you can press and hold the shift key and then move around the board with the arrow keys to "paint" that color across cells.

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) errors are highlighted with cell or digit colors, and correct completed numbers are indicated as well. Note this does not ensure that they are correct in the final solution, just that they are correct with respect to the rules. 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: []).

Slitherlink (スリザーョンク) is a classic Japanese logic puzzle published by Nikoli. In Slitherlink, the board begins with a set of cell vertices, with many of the cells containing numbers indicating how many lines between vertices must border that cell. The full set of rules below involve these lines and the numbers and how to complete a solve.

1. A cell with a number within it must contain that number (between zero and three) of lines on its borders. Cells without numbers can have any number of lines.
2. The lines between cells must connect to form a complete loop around the board that never crosses or touches itself.
3. There can only be one complete loop in a successful solution.

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 digit contents (0-3), 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. Digit 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 Slitherlink 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!