Optimise a modded Minecraft server

Lag on a modded server has a different mix of causes than lag on Paper. This guide covers the levers you have on Fabric, NeoForge, Forge and Quilt servers, which show a Mods tab: lower distances, a few performance mods, pre-generated terrain and a shorter mod list.

Checked against the Modrinth listings for Lithium 0.26.2, FerriteCore 9.0.0, Krypton 0.3.2, spark 1.10.187 and ModernFix 5.27.89+mc1.20.1 (its newest file for a 26.x version is 5.27.24+mc26.1.2), October 2026.

Measure before you change anything

Open the Console tab and read the TPS card, headed "Ticks per second", with its target of 20. A server that holds 20 is keeping up. If it sits below that when players are online, work through the steps below, and check the TPS card again after each one so you know what helped.

To find the cause rather than guess, install spark and profile. spark lists Fabric, Forge, NeoForge and Quilt as loaders on Modrinth. After installing it and restarting, run spark profiler start --timeout 120 in the Console. Profile a modded Minecraft server with spark walks through reading the report.

Lower the distances first

The Config Editor has the two settings that cost the most, in its Performance section.

1. Lower Simulation distance (chunks) first, because it is the cheaper of the two to cut. It controls how far from players mobs, crops and redstone keep running, and its default is 10.
2. Then lower View distance (chunks), default 10, if the server still struggles. It controls how much world data is sent to each player.
3. Press Save changes and restart the server.

Add performance mods

Open the Mods tab, choose Store, keep the Modrinth source selected and search for each name. The store starts filtered to your server's Minecraft version and, on Fabric, Forge and NeoForge, to your loader. Press Install and restart the server when the toast tells you to. Add them one at a time and recheck TPS between each.

Lithium has no Forge listing, so on Forge start with FerriteCore and ModernFix, if the store has a file for your version. On Forge that may be neither: FerriteCore's Forge files stop at Minecraft 1.20.1 and ModernFix's at 1.20.2, so a Forge server on 1.21 or 26.x has no file for either. ModernFix had no file for Minecraft 26.2 or 26.3 on any loader when we checked. If the store shows no file for your version, skip that mod for now.

Pre-generate your world

Chunky pre-generates chunks, so the server does not have to build new terrain while players explore. It lists Fabric, Forge and NeoForge among its loaders. Pre-generate a Minecraft world with Chunky has the commands and a sensible radius.

Trim your mod list

Every mod adds work at startup and during play. Open the Installed view and press Disable on mods you do not use, then restart. Disabling renames the file, so you can switch it back on. Remove a mod from your Minecraft server covers deleting one for good. Check for updates in the same view finds newer builds of the mods you keep.

What we set for you

You cannot edit the Java flags or heap size on Minecraft servers. We build the start script with Aikar's G1GC flags and size the heap from your plan's RAM at every start, so there is nothing to tune there. The Performance - auto-tuned card in JAR Manager shows the result. Your RAM is fixed by your plan, so a leaner mod list and shorter distances are the levers you have. How much RAM does my Minecraft server need? explains what to expect.