There are several ways to create and remove bridges. The user can start at a circle and drag the left mouse towards one of the four directions to indicate the creation of the bridge in that direction. The environment will extend the bridge to the next nearest circle, and will not allow the user to create illegal bridges (i.e. in the direction of a wall with no other circles, or into another perpindicular bridge). Alternately you can use the arrow keys to move around the board, and hold down the shift key followed by an arrow key to create a bridge in that direction. Or, you can press one of the directional keys N, S, E, W to create a bridge in that direction. Once a bridge has been created, the user can left-click on it a second time to double-bridge it, or a third time to delete it. Or the right-mouse click can remove a bridge. Pressing the directional key N, S, E or W converts a single bridge in that direction to a double bridge, or erases a double bridge.

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: []).

Hashiwokakero (橋をかける or "Build Bridges!"), is a classic Japanese logic puzzle published by Nikoli. In Hashiwokakero, the board begins with a collection of numbers in circles that must be connected. The numbers indicate how many "bridges" must connect that circle to its horizontal and vertical neighbor circles. Each circle can have zero, one or two bridges in each of the four directions. The rules below relate to those numbers and how to complete the puzzle.

1. A digit indicates the number of bridges between this circle and its neighbors to the north, south, east and west directions.
2. Circles can be connected with one or two bridges in any direction.
3. Bridges can not intersect other bridges.
4. All cells must, in the end, be connected into one contiguous group of circles.

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:<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 circles, from 1-8, 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. A dot '.' can be used as a visual separator, for example between rows. An example descriptor is as follows for entry 1: 'descr'.

For Hashiwokakero 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!