This is a level editor for Flywrench4k, an entry in the Java4k 2013 competition.
To try the levels that you build, first "save" them by pressing "S" and copy-pasting the text in the popup window. Next, click the link above to go back to the game and then press "L" in the game to load your level (by pasting the text).
Instructions for using the editor are available in the editor window.
Flywrench4k is based on indie developer messhof's excellent Flywrench, with permission from the author. The 4k version was made by Måns Olson.