ZstdMC

The mod replaces the compression and decompression modules that Minecraft uses for network traffic with Zstandard, a compression library that reaches higher compression ratios than the built-in method. Its stated goal is to cut the data sent between server and players in multiplayer, with the author reporting savings of roughly 40% to 90% of network traffic. The gains are described as applying to most scenarios, and the author notes that the change can affect stability and performance in some cases.

Installation is a matter of placing the mod file in the mods folder on both the server and each client. The server's server.properties file also needs a parameter adjusted: network-compression-threshold should be set to 128 or higher, which enables the compression path that ZstdMC changes. The author recommends the Fat version for most cases, because it bundles the libraries the mod needs. The project is open source under the MIT License, with its source code and issue tracker published, and it is released for NeoForge on 1.21.1 only.