To draw a path, left click on the center of a cell to begin. From there, drag the mouse in the direction to create the path. The path will draw as the dragging continues. Alternately, once on the board, you can press the shift key and hold while moving around the board with the arrow keys. In addition, you can enter a key to indicate the type of path desired for that cell (and into its neighbors). These keys are as follows, and will extend the line into the center of the adjoining cells:

• '-' key to draw a full horizontal line through the cell
• '|' or 'I' key to draw a full vertical line through the cell
• 'L','J','7', or 'F' key to draw a correspondingly shaped turn in the cell

Once created, a path can be removed by pressing the backspace key within a white cell. This deletes it just for this cell, but deletes the "arms" into the adjoining cells. You can also attempt to redraw with the left-click dragging method.

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 and completed rules are highlighted with digit colors. In some cases the solve difficulty will greatly decrease in Assist Mode (2), 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). The following puzzle codes have demos, which will walk you through a solve to help you on the path to mastery: []).

Masyu (ましゅ), is a classic Japanese logic puzzle published by Nikoli. In Masyu, the board begins with a collection of white and black circles. These circles have rules about a path that must be drawn through them. The final path drawn must go through all circles, and must for a continuous loop. The rules below relate to those circles and how to complete the puzzle.

1. A white circle must be traveled straight through by the path, with no change of direction. In addition, the path must turn in either of the squares before or after the circle in the direction of the path.
2. The path going through a black circles must turn in that square, and must continue at least one more square in both directions.
3. All circles must be completed with the path.
4. Not all squares without circles require the path to go through them.

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:<circle-descriptor>", where W is a number indicating the width of the grid, and H the height. The circle descriptor is a list of the pre-defined circle contents plus the spaces in between them, from left to right, then top to bottom. For the circles, the number 1 is used to indicate a white circle; 2 for a black circle. 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. A dot '.' can be used as a visual separator, for example between rows. An example descriptor is as follows for entry 1: 'descr'.

For Masyu 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!