SlitherLink puzzles are normally built on a rectangular grid (although other shapes are possible). The grid is defined by an array of dots which represent the corners of the cells within the grid. Some of the cells in this grid contain a single digit number between 0 and 3 inclusive. The remaining cells are blank.

To solve such a puzzle, the solver must join selected dots with horizontal and vertical lines so that a single loop is formed which does not cross over itself. If a cell contains a number, then that number of sides of the cell must be included within the loop.

The puzzles have unique solutions, and no guessing is required to complete the solution.

The following graphics show a Slitherlink puzzle in the Crossword Express Solve screen and a PNG graphic file produced by the program's print function, showing the complete puzzle solution. See also a  full size version of a PDF file. 

The key features of the Crossword Express Slitherlink Construction function are as follows:-
  • Fully automatic construction of puzzles.

  • Puzzles may be built in sizes ranging up to 50x50.

  • An option is available to allow the construction of both symmetrical and non-symmetrical puzzles.

  • A multi-build function allows the construction of many puzzles (thousands if necessary) in a single operation.

  • Fully manual construction is also available. This allows puzzles found in the printed media to be entered into Crossword Express.

  • Puzzles can be printed in an unprecedented range of user controlled colors and formats. Output can be sent direct to the printer or, if you install the appropriate software, it can be sent to a PDF file. The recommended software for this purpose is  Primo PDF which you can download free from their website,  although you might consider sending them a small donation if you find their program useful. Mac users will be able to create a PDF file directly from the screen provided by the printer driver.

  • Formatted output can also be exported from the Print screen to graphic files which conform to the BMP, GIF, JPG or PNG formats.

  • A fully interactive Solve function is available to allow you to solve the puzzles "on screen" without needing to print them.