ModernFix Modpack 1.16-1.20 Mod [1.21.4, 1.21.1, 1.21]

ModernFix Performance Improvements and Memory Reduction for 1.16–1.20

ModernFix is a comprehensive mod that enhances performance, lowers memory consumption, and resolves numerous bugs across modern Minecraft versions (most releases from 1.16 onward are compatible) without heavily altering the gameplay feel. When installed, most Forge modpacks for versions 1.16 through 1.19.2 see roughly twice the launch speed. With certain non‑default settings enabled, large modpacks such as All The Mods 8 can operate with 3 GB or less of allocated RAM.

This mod is free and open‑source. The entire source code is available on GitHub.

Technical Summary of ModernFix Game Optimizations

What exactly does ModernFix change under the hood? The mod applies a large number of tweaks – far too many to list here. The following is a concise overview of the main categories of improvements:

Backports of bugfixes from newer versions of Minecraft and/or Forge, e.g. fixing worlds breaking when you remove a dimension mod in 1.18 .
Patches to mods that are no longer supported on a given Minecraft version, to improve the gameplay experience instead of requiring players to update.
Many optimizations & improvements to the game's launch process to significantly improve speed and reduce random concurrency crashes.
Additional debug tools to help modders and players determine the cause of some rare game crashes/freezes, instead of relying on a painful mod bisection process.
It's not enabled by default due to compatibility issues, but ModernFix includes functionality to completely redesign the game's model loading system , replacing it with a new, dynamic version that loads models on the fly. Model loading is one of the major performance regressions to modded Minecraft that has been present since 1.8, and this new system alleviates nearly all of the downsides, bringing memory usage and loading times more in line with how they were in 1.7.10.
Need to play the vanilla game with very little RAM allocated (e.g. 512MB or less)? Now you can do that. Head to the "Ultra-Low Memory Footprint" page on the wiki .

Further Patch Details and Documentation

If you are technically inclined and would like a more complete breakdown of each patch, please refer to the Summary of Patches wiki page.

🐛 Where to go when something doesn't work

Please either report an issue on GitHub , or join the Discord and ask in the #modernfix-discussion channel. Be sure to mention the Minecraft version, modloader, and ModernFix version you are using, as well as what other mods you have installed.

Supporting the ModernFix Development Project

You can help sustain ModernFix development in two primary ways:

Spread the word! Test ModernFix in modpacks and encourage them to include it.
If you feel generous, I do accept donations via Ko-fi . Donating is not required (as ModernFix is free), but every little bit helps. I work on ModernFix in my spare time, so any compensation I receive helps to sustain development.

Recommended Companion Mods for ModernFix

Minecraft has many performance mods available, and listing them all is impractical. However, here are a few that I personally consider essential:

On any version before 1.19.4 you should always have LazyDFU installed, as it eliminates the incredible lag caused by the DFU system.
On any version before 1.20 you should generally use Starlight unless it has a compatibility issue with your mods (which is quite rare). It offers vastly improved lighting performance and can also fix FPS stutters when moving between chunks.
Always have FerriteCore installed, as Mojang's implementation of blockstates/models is laughably inefficient, and quickly consumes RAM as soon as more content is added beyond what vanilla offers.
Install a mod like Shutup Experimental settings (before 1.19) or Yeetus Experimentus (1.19+). These mods will suppress the pop-up screen about experimental game features, which otherwise causes the game to reload its resources twice.

OptiFine Alternatives and Compatibility Note

On a related note: I do not advise using OptiFine in any modded environment. It is closed‑source, patches the game in ways that often break Forge and other mods, and significantly increases launch times (sometimes by several minutes). Consider using Sodium on Fabric or Embeddium on Forge instead. ModernFix does not officially support OptiFine, and using them together may cause issues.

How to configure ModernFix on a server

Common Questions