What Geyser does
Geyser is a proxy that sits between Minecraft: Bedrock Edition clients and Minecraft: Java Edition servers. It translates the network packets the two versions use so a Bedrock player can join a Java server. GeyserMC is direct about the trade off. This is packet translation between two different games, so not everything behaves exactly like native Java.
It's an Open Collaboration project. The official listing credits Ziax, the group behind CubeCraft Games, and thanks the earlier DragonProxy project for its work on protocol translation.
Who it's for
Server owners running a Java Edition server who want Bedrock players to connect. On Hangar, Geyser is marked as server side required and client side unsupported. So that matches how it runs. And it lives on the server or proxy, not on the player's device, and the Bedrock player connects with an unmodified client.
Running it
You've two paths. Install Geyser as a plugin on Paper, Waterfall, or Velocity, or run it as a standalone program. GeyserMC notes that plugin installs usually work right away, while standalone setups can need extra steps.
Check one thing with your host first. Bedrock connections use UDP, not the TCP that Java uses, and some hosts block UDP by default. Real talk, geyserMC keeps a page on hosting providers and how Geyser works with each.
Floodgate
Floodgate is a separate companion plugin. And it removes the requirement for Bedrock players to also own and log into a Java Edition account. They still need a valid Microsoft account. Without Floodgate, Bedrock users need a Java account to join.
Versions
Hangar lists supported Java Edition versions individually rather than as a range: 1.13, 1.13.1, 1.13.2, 1.14, 1.14.1, 1.14.2, 1.14.3, 1.14.4, 1.15, 1.15.1, 1.15.2, 1.16, 1.16.1, 1.16.2, 1.16.3, 1.16.4, 1.16.5, 1.17, 1.17.1, 1.18, 1.18.1, 1.18.2, 1.19, 1.19.1, 1.19.2, 1.19.3, 1.19.4, 1.20, 1.20.1, 1.20.2, 1.20.3, 1.20.4, 1.20.5, 1.20.6, 1.21, 1.21.1, 1.21.2, 1.21.3, 1.21.4, 1.21.5.
Known limits
GeyserMC is upfront that some features can't be matched because Bedrock and Java differ. The GitHub readme lists movement that isn't yet near perfect and some entity flags as open work, and a separate limitations page covers the rest.
License and build
Geyser is MIT licensed. Its readme names the libraries it builds on: the Adventure Text Library, the CloudburstMC Bedrock Protocol Library, GeyserMC's own Java Protocol Library, TerminalConsoleAppender, and slf4j.
If you want to see it work before installing anything, GeyserMC runs a test server at test.geysermc.org, port 25565 for Java and 19132 for Bedrock.
