A modded server does far more work per tick than vanilla, and one of the cheapest ways to claw some of that back is a small set of mods whose entire job is to make the server run faster. They rewrite inefficient parts of the game so the same tick costs less, without changing how the game plays for anyone connecting. This post explains the categories worth knowing, names the well-established ones where we are confident, and is honest about where the right name depends on your exact loader and version. It assumes you have already picked a loader, which is covered in choosing a mod loader.
One thing to settle first. Most of the mature server-side optimisation mods grew up on Fabric, and many now have NeoForge ports or equivalents, so this post talks mainly about those two loaders. Forge has fewer options, though a Forge pack can still be tuned through its configs and the general steps in optimising modded Minecraft. Whatever you run, these mods reduce the cost of work the server already does. They do not add a second tick thread, so the single-thread ceiling underneath is still there.
The categories that matter
Rather than a shopping list, it helps to think in categories, because the specific mod names change with each Minecraft version and loader but the jobs stay the same.
Memory reduction is the quietest win. Some mods change how the game stores its data in memory so the server holds the same world in less heap, which means fewer and shorter garbage-collection pauses. On a heavy pack that loads a huge number of blockstates and objects, this is worth having even though you never see it directly. FerriteCore is the well-known one in this category, and it is commonly safe to run. As of Minecraft 1.21.x it is available for Fabric, NeoForge and Forge, and stays actively maintained.
Chunk and lighting optimisation targets two of the most expensive things a server does. Generating terrain and calculating light are heavy, and mods in this category make both cheaper, either by rewriting the lighting engine or by spreading chunk work more efficiently. Starlight was the established Fabric lighting rewrite, but the standalone mod stopped at Minecraft 1.20.4. On 1.21.x its light-engine work now lives in Moonrise, the successor for Fabric and NeoForge, which bundles a rewritten chunk system alongside the light engine. C2ME is the well-known standalone chunk mod that parallelises parts of the chunk pipeline, and it is available for Fabric and NeoForge on 1.21.x. Moonrise overlaps with both Starlight and C2ME, so treat those as competing approaches rather than a set to stack together. These pair naturally with pre-generating the world, which does the same job from the other direction and is covered in world management and pre-gen.
Entity and AI optimisation goes after one of the biggest tick costs on a busy modded server. Mobs, farm animals and the creatures mods add all run pathfinding and behaviour logic every tick, and in a packed base that dominates the profile. Mods in this category make that logic cheaper or skip it when it cannot matter. As of Minecraft 1.21.x most of this is covered by the general patch mods rather than one dominant standalone mod: Lithium rewrites mob AI and brain selection, and its rules do the bulk of the entity work on both Fabric and NeoForge. If you want to go further, Adaptive Performance Tweaks throttles AI and mob activity dynamically when TPS starts to drop. Some of this overlaps with the general patches, so read what each one actually changes before you stack them.
General patches are the broad category: a single mod that rewrites many small inefficiencies across the game's own code, from block ticking to collision to redstone. Lithium is the best-known general server-side optimisation mod, originally on Fabric and now with an official NeoForge build too, and it is the one most performance-focused packs reach for first. As of Minecraft 1.21.x it is available for both Fabric and NeoForge. Alternate Current is a well-regarded rewrite of the redstone logic specifically, if your players build heavy redstone, and it is available for Fabric and NeoForge on 1.21.x.
Server-side and client-side are not the same
This is the caveat that saves the most wasted effort. Optimisation mods split into server-side and client-side, and the two do completely different jobs. Client-side mods like the popular rendering optimisers improve frame rate on a player's machine and do nothing at all for your server's tick. Installing them on the server is pointless, and in a pack that expects them on the client they belong in the client files, not the server pack. The mods in this post are the server-side ones, the ones that lower MSPT. When you read that a mod "improves performance", check which side it acts on before you put it on the server.
Some of these change behaviour, so test them
A performance mod earns its place by making the tick cheaper without a player ever noticing. Most of the mature ones are careful about that, but some optimisation mods change behaviour in small ways, an entity that acts slightly differently, a redstone edge case, a farm that runs at a different rate. On a technical or long-running server those differences can matter. So treat every optimisation mod as a change to test, not a free win to trust. Add them a few at a time, profile a busy window with a profiler like spark before and after, and watch for anything your players report as different. A mod that saves two MSPT is not worth it if it quietly breaks a build people spent weeks on.
Mods do not replace right-sizing the pack
The last point is the one that keeps expectations honest. Optimisation mods reduce the cost of the work the server does, but they do not remove the work. If a pack is simply too heavy for the box, or a base has a thousand always-loaded chunks running machines around the clock, no mod list rescues it. The bigger levers are still right-sizing the pack to the hardware, keeping view and simulation distance sensible, capping entities, and pre-generating the world so terrain is not built live. Those are the foundation, and the general tuning that goes with them is in optimising modded Minecraft, with the whole server stack laid out in the running a Minecraft SMP pillar. Performance mods sit on top of that foundation and make a well-tuned server better. They cannot fix a badly-sized one.
Run the server-side ones your loader supports, add them carefully, profile the difference, and you will get real tick time back on a heavy pack. Just keep them in their place, which is one layer of a stack that starts with the box underneath.
If you want that box built for the single-thread load modded Minecraft puts on a server, that is what we run.