Compact Machines Preview Fixer
Fixes the severe memory leak when previewing Compact Machines rooms. Opening a preview can chew through hundreds of MB to multiple GB of RAM that never…
⬇ Download on CurseForgeThe author built this one for Minecraft 1.21.1 on NeoForge. On other versions it may install and then do nothing.
The problem
Right clicking a Compact Machine without a Personal Shrinking Device pops up a little 3D preview of what is inside. Handy! Except every time you open one, the game grabs a huge chunk of memory to draw it, and then never gives that memory back when you close the preview.
Open a few previews of a small machine and your RAM use creeps up. Open a single preview of a big machine (a 45x45x45 room can use a full gigabyte of RAM), and your game can freeze for minutes or crash outright. Open one with a packed Mekanism or Oritech setup inside and you can blow past 50 GB of committed memory in a single click.
Worse, normal heap memory tools show nothing wrong, because the leak is in off heap / GPU memory. Most players just see "Minecraft is eating all my RAM" and have no idea why.
What this mod does
When you open a preview, this mod hooks into the screen and makes sure the memory the preview reserved is properly released as soon as either of the following happens:
- You close the preview.
- The preview screen swaps in a new preview.
That is it. No new blocks, no new items, no menus, no config. You install it, the leak stops happening.
Symptoms it fixes
- Game freezing for several seconds (or minutes) when previewing a large or busy compact machine.
- Minecraft's RAM usage climbing every time you open a preview and never going back down.
- Out of memory crashes after opening a few previews in a single play session.
- Whole PC becoming sluggish because Minecraft has eaten all available memory.
If any of those sound familiar, this mod is for you.
Client side only. The leak is in the preview rendering code, which runs on your computer. You do not need to install this on the server. It will not desync you from other players.
Safe to add to or remove from existing worlds at any time.
Compatibility
- Minecraft: 1.21.1
- Loader: NeoForge 21.1.55 or newer
- Requires: Compact Machines (any 1.21.1 version that still has the broken preview)
If Compact Machines is not installed, this mod does nothing and stays out of the way.
When can I uninstall this?
As soon as Compact Machines itself ships a fix for the underlying preview leak, you can safely remove this mod. Until then, leave it in.
- Ships as cmpreviewfixer-21.1-1.1.0.jar — drop this file into the mods folder
- Download size: 9 KB
- Download link checked 23 Aug 2026 — working
These come from our own check of the pack file, not from the source page.