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+# LauncherJava `launcherjava/`
+
+> **Location**: `launcherjava/`  
+> **Language**: Java  
+> **Purpose**: Minecraft launching component
+> **Latest Version**: 0.0.5-1
+
+---
+
+## Overview
+
+LauncherJava is the Java-based component responsible for actually launching Minecraft. It acts as an intermediary between the C++ launcher and the Minecraft JVM process.
+
+---
+
+## How It Works
+
+```
+┌─────────────┐      ┌──────────────┐     ┌─────────────┐
+│  ProjT      │────▶│ LauncherJava │────▶│  Minecraft  │
+│  Launcher   │      │   (Java)     │     │    JVM      │
+│  (C++)      │      │              │     │             │
+└─────────────┘      └──────────────┘     └─────────────┘
+      │                    │
+      │   stdin            │   exec
+      │   (script)         │   (launch)
+      ▼                    ▼
+```
+
+### Launch Sequence
+
+1. C++ launcher sends launch script via stdin
+2. LauncherJava parses the script
+3. Waits for `launcher` command
+4. Executes Minecraft with configured parameters
+
+---
+
+## Launch Script Format
+
+The launcher communicates via a text-based protocol:
+
+```text
+mod legacyjavafixer-1.0
+mainClass net.minecraft.launchwrapper.Launch
+param --username
+param PlayerName
+param --version
+param ProjT Launcher
+param --gameDir
+param /path/to/minecraft
+param --assetsDir
+param /path/to/assets
+param --assetIndex
+param 1.20.4
+param --uuid
+param xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx
+param --accessToken
+param [TOKEN]
+param --userType
+param msa
+windowTitle ProjT Launcher: Instance Name
+windowParams 854x480
+userName PlayerName
+sessionId token:[TOKEN]:[UUID]
+launcher standard
+```
+
+### Commands
+
+| Command | Description |
+|---------|-------------|
+| `mod <name>` | Load a mod (tweaker) |
+| `mainClass <class>` | Set main class |
+| `param <value>` | Add launch parameter |
+| `windowTitle <title>` | Set window title |
+| `windowParams <WxH>` | Set window size |
+| `userName <name>` | Player username |
+| `sessionId <id>` | Session identifier |
+| `launcher <type>` | Execute launch |
+| `abort` | Cancel launch |
+
+---
+
+## Launcher Types
+
+| Type | Use Case |
+|------|----------|
+| `standard` | All Minecraft versions (recommended) |
+| `legacy` | Minecraft < 1.6 (deprecated) |
+
+### Differences
+
+- **Standard**: Universal launcher, works with all versions
+- **Legacy**: Supports custom window icon/title but only for old versions
+
+---
+
+## Building
+
+LauncherJava is built as part of the main CMake build:
+
+```bash
+# Built automatically with main project
+cmake --build build
+
+# Or build separately
+cd launcherjava
+./gradlew build
+```
+
+---
+
+## Debugging
+
+### Enable Debug Output
+
+```text
+debug on
+mainClass ...
+```
+
+### Attach Profiler
+
+Since LauncherJava waits for the `launcher` command, you can:
+
+1. Start LauncherJava
+2. Attach your profiler (VisualVM, JProfiler, etc.)
+3. Send the `launcher` command
+
+---
+
+## License
+
+Available under **GPL-3.0** (with classpath exception), sublicensed from its original **Apache-2.0** codebase.
+
+---
+
+## Related Documentation
+
+- [Program Info](./program_info.md) — Application identity
+- [JavaCheck](./javacheck.md) — Java detection