Eaglercraft is a fan-made, open-source project that decompiles older versions of Minecraft and compiles them into JavaScript and WebGL. This allows the game to run natively inside any modern web browser like Google Chrome, Mozilla Firefox, Microsoft Edge, or Safari.
For those unfamiliar, Eaglercraft is a browser-based recreation of Minecraft (specifically Beta 1.5.2 through modern-style updates) built entirely in JavaScript and HTML5. It requires no plugins, no downloads, and no Java — just a web browser. “Unblocked 121” refers to one of the many hosting versions available on school or work-friendly proxy sites (like “121” being a common numeric alias for an unblocked games portal). eaglercraft unblocked 121