If you are trying to combine Eaglercraft Singleplayer with "Paper" (the high-performance server software), you are essentially looking to host a private environment that bridges browser-based gameplay with a stable backend.
It serves as a "Trojan Horse" for students, providing a private sanctuary of creativity in environments where every other creative outlet is often filtered or blocked. eagler craft singleplayer
Because Eaglercraft runs in a browser, saves are stored in your browser's Local Storage (IndexedDB). If you are trying to combine Eaglercraft Singleplayer
Eaglercraft is a popular open-source project that ports Minecraft Java Edition to run directly in a web browser eagler craft singleplayer