Lithium

Lithium speeds up the server. It handles what happens in the game in the background: mob movement, water and lava behavior, block processing, memory management. The result is that the server can handle more players and more entities without the game slowing down.

Most important is where it belongs: Lithium is installed in the mods folder on the server, and players don't need to install anything. It's one of the few mods that benefits the server itself — those who look for it usually do so because their server can't keep up.

Lithium itself doesn't add or remove anything: there are no new blocks, commands, or in-game settings in it. When done well, players don't even know about it — their smoothness just improves and it happens less often that the server freezes for a moment.

For it to work, you need Fabric (or NeoForge — depending on the version). On a server with Fabric, Lithium goes in the same folder as other mods. Players connecting from a vanilla client don't need to change anything.

Watch out for one thing: Lithium changes the game's physics and logic, even if invisibly. On a server where datapacks or mods are running that rely on exact original behavior (for example, very specific farms), they may stop working as players expected. It's worth going through it with active players after installation.

1. Lithium is a server-side mod — it is installed in the mods folder on the server, players do not install anything.
2. Install Fabric Loader (or NeoForge) on the server for your Minecraft version.
3. Download Lithium from modrinth.com/mod/lithium in the version exactly for your game version and loader.
4. Stop the server and back up the world and the mods folder — it’s a few seconds of work after every mod change.
5. Upload the .jar to the mods folder on the server.
6. Start the server and check the console: Lithium must load without errors.
7. Verify that the server is running and players can connect (players from a vanilla client need nothing).
8. Measure load before and after: what percentage of CPU the server uses with the same number of players and entities.
9. Go through with players the farms and mechanics that depend on exact game behavior (item movement, water behavior).
10. If something breaks, remove Lithium and compare — it’s the fastest way to find out who is responsible.
11. When updating the game to a new version, replace Lithium with the version for the new version, otherwise the server will not start.

Lithium belongs on the server, not with players. If you also put it in the client, you won't break anything, but players don't need to install anything — tell them that, and you'll save questions.
Lithium doesn't add anything to the game (no blocks or commands), so after installation you won't see anything new. Success is recognized by lower load.
It changes minor details in game logic. Farms and mechanics that depend on exact original behavior may behave differently — go through them with players.
The version must match the game version and loader. After updating the game, a server with incompatible Lithium won't start.
It combines with Sodium (that one is on the players' side) — one speeds up the server, the other rendering on the player's side. Together, the difference is most noticeable.
Measure load before and after, so you have something to prove it helped the server. Without measurement, you're just arguing about the benefit.
If something doesn't work after installation, remove Lithium first — the elimination method is fastest here.