FermiumBooter
by fonnymunkey
Developers who need to change Minecraft or Forge classes can use FermiumBooter, a Forge library that loads mixins both early and late in the startup sequence.
What it does
Mixins queued through FermiumBooter can be applied either early, before most classes load, or late, after mods are initialized. This makes it possible to modify vanilla and Forge classes as well as classes belonging to other mods, which a mixin loaded at one fixed point could not reach.
A @MixinConfig annotation extends the Forge @Config system, so a mixin can be queued automatically when a config toggle is switched on. Developers can also declare which mods a mixin requires or is incompatible with, and FermiumBooter checks those conditions before applying it. A mixin that fails the check can be skipped, with a logged warning or an in-game warning that can be turned off.
The library is published for Forge only, for Minecraft 1.12.2, with version 1.5.3 as the latest file, dated 2026-10-11. It is open source under the GNU Lesser General Public License v3.0 or later. Either side can load it: the client alone, the server alone or both, and neither side needs it. Other Forge mods such as FermiumASM, RLFoliage, ShieldBreak and FermiumMixins depend on it, so it is installed alongside them.
Key features
Early and late mixin queues
Mixins can be enqueued to apply before or after the point where most mods are loaded.
Config-driven mixin enqueueing
The @MixinConfig annotation queues a mixin automatically based on a Forge config toggle.
Compatibility declarations
Developers list the mods a mixin requires or conflicts with, and the check runs before the mixin is applied.
Warnings for failed checks
A failed compatibility check is logged, can force the mixin off, and can show an in-game warning that players may disable.
Supplier-controlled mixins
A Supplier decides whether each enqueued mixin is applied, giving developers control over optional mixins.
Compatibility
Latest build for each game version and loader.
Only full game releases are shown. This mod publishes no snapshot builds.
Required by 24 mods
Use cases
Patching classes from other mods
A developer can modify a class that another mod defines, which a standard mixin applied at one stage cannot reach.
Optional mixins behind config options
A mod can ship a mixin that is applied only when a player enables the matching option in its config file.
Who it’s for: Forge mod developers who write mixins for Minecraft 1.12.2 and need them applied at different load stages, or only when another mod or config setting is present.
How it compares
Twelvefold Booter is a Forge library for 1.12.2 under the MIT License, open source and optional on either side. MixinConBooter covers 1.6.1 – 1.12.2 on Forge, also under the MIT License and open source. MixinBooter is a client and server mod for 1.8 – 1.12.2, released under the GNU Lesser General Public License v2.1 only, so both sides must run it.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| FermiumBooter | Forge | 1.12.2 | Client or server, optional | 2026-10-11 |
| Twelvefold Booter | Forge | 1.12.2 | Client or server, optional | 2025-05-15 |
| MixinConBooter | Forge | 1.6.1 – 1.12.2 | Client or server, optional | 2025-09-26 |
| MixinBooter | Forge | 1.8 – 1.12.2 | Client and server | 2026-10-12 |
Questions
Which Minecraft version does FermiumBooter support?
Does FermiumBooter need to be installed on the server?
Which mods require FermiumBooter?
In the catalog
FermiumBooter is one of 3,514 Library mods on ModsFinder, and one of 1,576 Library mods for Forge. 2,920 mods support Minecraft 1.12.2.
More from fonnymunkey
Similar mods
What the author says
FermiumBooter is a mixin mod utility to allow developers to load mixins both early and late, allowing for modifying classes that normally could not be modified otherwise. Current features include; - Enqueue mixins to be applied both early and late, to allow for for modifying Vanilla/Forge classes, as well as mod…
Official listing
- Modrinth page
- modrinth.com/mod/fermiumbooter
- Owner
- fonnymunkey
- Published
- 2024-01-29
- Updated on Modrinth
- 2026-10-11
- Facts verified
- 2026-10-15