Eaglercraft does include Mojang's copyrighted assets. You must own a legitimate copy of Minecraft Java Edition and use the provided tools to extract assets from your local .minecraft folder. The code itself is a clean-room reimplementation, distributed under an open-source license for educational and personal use.
Here is how to use the GitHub server software: eaglercraft 1.12 2 github
Are you interested in learning how to connect to Eaglercraft? Share public link Eaglercraft does include Mojang's copyrighted assets
: You can "Download ZIP" from the repository, extract it, and open the index.html file in any modern browser (Chrome or Firefox are recommended). eaglercraft 1.12 2 github