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Improved Cleanroom Relauncher
Makes the Cleanroom Relauncher a much more seamless experience for modpack users and allows modpack creators to not have to worry about setup instructions! It will automatically download the required java version and cleanroom libraries, and configure it automatically for you!
Relaunches a Forge 1.12.2 instance with Cleanroom Loader, with a streamlined first-run experience and automatic Java setup.
Features
- Automatic Java download and setup
- Configurable major version (default: 24)
- Configurable distribution (default: Adoptium)
- Cross-platform and arch-aware
- Windows: x64, ARM64
- Linux: x64, aarch64
- macOS: Intel (x64), Apple Silicon (aarch64)
- First-run automation
- Auto-selects the latest Cleanroom Loader release
- Progress popup: "Setting Up Necessary Libraries (Only Happens Once)" with download progress
- Auto-switch Java when config javaVersion changes
- Automatic download resuming and retrying
First run setup
- If no Java path is configured, the relauncher downloads Java for your OS/architecture and config javaVersion.
- A progress dialog shows the download status and then the archive is extracted automatically.
- The latest Cleanroom Loader release is selected automatically (no manual selection needed).
Configuration
- File: config/relauncher.json
- Key options:
- javaVersion: desired major version (e.g., 21, 24). Changing this triggers an automatic re-download and switch.
- javaExecutablePath: set if you want to force a specific Java. If it’s not valid or mismatched with javaVersion, the relauncher will auto-download the correct one.
Cache locations
- Java is cached under: <UserHome>/.cleanroom/relauncher/java/<distribution>-<version>-<os>-<arch>
- Example: ~/.cleanroom/relauncher/java/temurin-21-windows-x64
- Example: ~/.cleanroom/relauncher/java/graalvm-22-linux-x64
- Example: ~/.cleanroom/relauncher/java/graalvm-24-mac-aarch64
It offers a GUI on the client for manual configuration when the autoconfiguration fails.
Cleanroom Loader is a new loader developed from the roots of Forge Mod Loader for Minecraft 1.12.2 specifically. It boasts better performance, modern Java support, and offers better experiences for mod developers.
All Versions
+ Add Version
[0.3.8] Improved Cleanroom Relauncher 0.3.8
by Unknown on Mar 16, 2026
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### Changed
- Default Java version to 25 due to newer versions of Cleanroom requiring it
- Automatically upgrade configured Java version to 25 when Cleanroom version is 0.5 or newer
[0.3.7] Improved Cleanroom Relauncher 0.3.7
by Unknown on Mar 04, 2026
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### Added
### Fixed
### Changed
## Upstream Changes
### Fixed
disableCacheTTLoption in config to bypass release network checks.cacheDiroption in config to specify a custom cache directory.
### Fixed
- HTTP 403 API rate limit crashes when checking releases. Added a
User-Agentheader to requests and gracefully fallback to cached releases data.
### Changed
- Backend config parser to resolve file path and locale issues on some systems.
## Upstream Changes
### Fixed
- Stop scanning the entirety of /opt on Linux (updated JavaUtils to 1.1.5)
[0.3.6] !improved-relauncher-0.3.6.jar
by Unknown on Oct 20, 2025
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### Fixed
- NoSuchElementException Crash
[0.3.5] !improved-relauncher-0.3.5.jar
by Unknown on Oct 09, 2025
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## Hotfix 2: Electric Boogaloo
### Fixed
(Screw Rosetta man, that thing is just too aggressive, also due to Mojang's laziness)
### Fixed
- MacOS Architecture Detection Again
(Screw Rosetta man, that thing is just too aggressive, also due to Mojang's laziness)
[0.3.4] !improved-relauncher-0.3.4.jar
by Unknown on Oct 08, 2025
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## Hotfix
### Added
### Added
- Architecture Validation
[0.3.3] !improved-relauncher-0.3.3.jar
by Unknown on Oct 08, 2025
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### Fixed
(Delete config to download the correct version, or set javaPath setting to: "Null")
## Upstream Changes
### Added
### Fixed
### Changed
- MacOS Architecture Detection
(Delete config to download the correct version, or set javaPath setting to: "Null")
## Upstream Changes
### Added
- Respect the launcher's original heap space setting arguments (-Xms, -Xmx) if none is specified in the configuration
### Fixed
- Compatibility with newer MMC pack formats (starting from Cleanroom 0.3.19)
- Encode and decode configuration with UTF-8
- Some Linux installs not being detected properly (updated JavaUtils to 1.1.3)
### Changed
- Thanks to @ZZZank, using MethodHandles to call the wrapper class's main method instead of standard reflection, allows for a cleaner stacktrace
[0.3.2] !improved-relauncher-0.3.2.jar
by Unknown on Oct 04, 2025
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### TLDR:
Faster more reliable downloads, auto-update, and auto-cleanup.
### Added
### Fixed
### Changed
Faster more reliable downloads, auto-update, and auto-cleanup.
### Added
- Multi-chunk parallel Java downloads
- Multi-file parallel library downloads
- Better download speed and ETA tracking for all downloads
- Better download resuming and retrying
- Java download verification
- Auto-Update
- Automatic cleanup of unused temp setup files
- Taskbar icon during download
### Fixed
- Library progress not showing
### Changed
- Default Java version from 21 to 24
[0.3.1] !improved-relauncher-0.3.1.jar
by Unknown on Sep 16, 2025
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### **Added:**
Run the game once to generate the updated config
- GraalVM support** _(Switch in config)_
- Partial Download Resuming**
- Automatic Download Retry on Fail**
- Download Speed and ETA display**
- Dark Mode** _(Togglable in config)_
Run the game once to generate the updated config
[0.3.0] !improved-relauncher-0.3.0.jar
by Unknown on Aug 28, 2025
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- Added auto Java download and configuration.
- Added OS and architecture detection.
- Windows/Linux/MacOS Support.
- ARM64/X64 Support.
- Auto selects latest Cleanroom Loader version and Java 21 on first launch, can be changed in config.
- Automatically switches Java when Java version changed in config.
- Download progress popup.
- Manual selection window now only appears when either detection or download fails.
