Class Loader Fixer
by HyperSpeeed
Class Loader Fixer repairs how legacy Forge versions set the CodeSource of loaded classes, a fault that misled tooltip mods such as Block Helper.
What it does
Old Forge versions set the CodeSource of loaded classes incorrectly, so mods that check where an item came from can treat modded items as vanilla. The mod is a simple jar mod that ships a backported RelaunchClassLoader, which replaces the built-in version in FML and allows mods to read file source classes. Block Helper is the example given for a mod that showed wrong item tooltips before the fix.
The mod is published for Forge only, across eight release versions 1.3.1 – 1.4.5, with 2 for 1.4.5 as the latest file, dated 2024-07-04. Installation requires removing the META-INF folder and overwriting existing files, so the fix is applied in place. It runs on the client alone, so servers do not need it. The mod is released under the MIT License and is not open source. Fabric versions exist, and the fix is also incorporated directly into Fabricated Legacy Forge, which is an alternative route. The author asks users to report incompatibilities through the issue tracker.
Key features
Backported class loader
A backported RelaunchClassLoader replaces the built-in version in FML, letting mods read the source of classes.
Corrected CodeSource
Classes loaded through the fixed loader carry a correct CodeSource, so procedures that rely on it behave as intended.
Overwrite install
The jar is applied by deleting the META-INF folder and overwriting existing files, with no separate patch step.
Compatibility
Latest build for each game version and loader.
This mod also publishes snapshot builds. Snapshots are not shown in the matrix.
Use cases
Item tooltip mods
Tooltip mods that check an item's origin, such as Block Helper, stop mislabeling modded items as vanilla on the affected versions.
Who it’s for: Players running Forge 1.3.1 – 1.4.5 who see wrong item information from tooltip mods. The fix matters only on those legacy builds, and players on newer versions do not need it.
How it compares
Universal FML is open source under the GNU Lesser General Public License v2.1 only, runs as a client or server optional mod, and is published for Forge across 1.8 – 26.3. Animation Crusher Fixer is server-side only and open source under the GNU Affero General Public License v3.0 only, targeting 1.20.1 on Forge. Class Loader Fixer is client-side only, uses the MIT License, and is not open source, so it covers a different and much older version range.
| Mod | Loaders | Game versions | Environment | Updated |
|---|---|---|---|---|
| Class Loader Fixer | Forge | 1.3.1 – 1.4.5 | Client-side only | 2024-07-04 |
| Universal FML | Forge | 1.8 – 26.3 | Client or server, optional | 2026-08-18 |
| Animation Crusher Fixer | Forge | 1.20.1 | Server-side only | 2025-11-02 |
Questions
Does Class Loader Fixer need to be installed on the server?
Which game versions does the fix cover?
Is Class Loader Fixer available for Fabric?
In the catalog
Class Loader Fixer is one of 36,990 Utility mods on ModsFinder, and one of 14,575 Utility mods for Forge. 131 mods support Minecraft 1.4.5.
More from HyperSpeeed
Similar mods
What the author says
This mod fixes the Class Loader in legacy versions of Minecraft. This is a simple jar-mod which adds the CodeSource to each loaded class in FML. That is actually everything this mod does (well, besides fixing a few more bugs on even older versions of Forge). This mod just ships a backported RelaunchClassLoader which…
Official listing
- Modrinth page
- modrinth.com/mod/class-loader-fixer
- Owner
- HyperSpeeed
- Published
- 2022-02-11
- Updated on Modrinth
- 2024-07-04
- Facts verified
- 2026-10-15