First you must have the following to use LilyTool:
Java Runtime Environment 1.4.2 or later
You can download it from its official website.
If you have this, run jEdit and choose Plugins>Plugin Manager..., select Install tab and check LilyTool. Click install and jEdit will automatically download and install all necessary files and plugins for you.
JEdit's Plugin Central doesn't always have the latest version of
LilyTool, because jEdit plugin repository is not updated so often, than
LilyPondTool. So you may like to download it from our project page.
Download the latest release of lilyj4edit,
along with the latest release of LilyJHelp,
and unzip them to the jars folder of your jEdit
installation directory. You may also have to install additional
plugins.
To update the the syntax coloring mode file, download the latest
release of the lilymode package, and unzip it to the
modes folder of the jEdit installation
directory.