MLRC - Minecraft Launcher of Rust Command-line

MLRC installs, configures and starts Minecraft: Java Edition from the command line. It fetches version metadata from Mojang, downloads only what that version needs, provisions the Java runtime the version declares, and launches the game.

Everything lives next to the executable, so the installation is a folder you can move or copy. The launcher is split into an engine (mlrc-core) and a CLI (mlrc-cli), so other tools can reuse the engine without touching it.

Features

• Install any vanilla version, one per command, with SHA1-verified downloads from Mojang or BMCLAPI
• Managed Java runtimes, one per major, so JAVA_HOME never breaks a version
• Portable: one folder holds everything, and nothing is written outside it
• Fabric, Quilt, Forge and NeoForge, installed through the same command
• Instances: a version that keeps its own worlds, mods, Java heap and account
• Mods, modpacks, resource packs, shaders and data packs from Modrinth and CurseForge
• Offline play under any name, Yggdrasil login for third-party servers, and Minecraft Unified Pass (Nide8)
• Several accounts per installation, and an instance may pick its own
• Background launches with a pid you can stop, resumable downloads, one writer per data directory
• Machine-readable output: exit codes, error codes, NDJSON events
• mlrc doctor for when something is wrong
• Microsoft account login

Requirements

• Windows, macOS or Linux
• No Java installation required - MLRC downloads and manages its own runtimes and ignores JAVA_HOME and PATH unless configured otherwise
• Disk: roughly 100-200 MB per Java runtime, 50-600 MB per Minecraft version

Install

Download an archive from the releases page and unpack it; the launcher is a single binary. From source:

cargo build --release
./target/release/mlrc --version

Usage

mlrc install 1.18.2        # asks before installing the Java 17 runtime
mlrc launch 1.18.2
mlrc use 1.18.2            # remember it for a bare `mlrc launch`
mlrc launch 1.18.2 --detach  # start it and get the terminal back; prints pid and log
mlrc stop                     # stop whatever is running in the background

Not sure which version to pick? --list prints them, newest first, and asks how many to show; with a loader, only the versions that loader has a build for:

mlrc install --list                       # asks: show the first (10/921) - or `all`
mlrc install --list --limit 0             # everything, no question
mlrc install --list --type release        # releases only
mlrc install --list --type april_fools    # the joke builds, 9 of them
mlrc install --list --loader neoforge --type release

Categories are release, snapshot, old_beta, old_alpha and april_fools; the last one is derived (a snapshot released on 1 April, plus the one that shipped on 31 March), because Mojang's metadata has no marker for it.

Modded. Loaders are installed by the same command, and the id it prints is what you launch:

mlrc install 1.21.1 --loader fabric       # or quilt
mlrc install 1.21.1 --loader neoforge     # or forge
mlrc launch fabric-loader-0.20.1-1.21.1

A second world set. Every version has its own folder, so an instance is what you want:

mlrc instance create survival --version fabric-loader-0.20.1-1.21.1 --memory 4G
mlrc launch --instance survival

Mods. Modrinth by default; required dependencies come with them.

mlrc mod install iris --instance survival      # also installs Sodium
mlrc mod list --instance survival
mlrc mod update --instance survival --check
mlrc mod disable lithium --instance survival    # renamed, not deleted

Content beyond mods. Resource packs, shaders and data packs install the same way, into resourcepacks/, shaderpacks/ and datapacks/:

mlrc pack search faithful --kind resourcepack --mc 1.21.1
mlrc pack install faithful-32x --instance survival
mlrc pack install complementary-reimagined --instance survival   # a shader
mlrc pack install terralith --kind datapack --instance survival --world MyWorld
mlrc pack list --instance survival

Modpacks. instance import installs the loader a pack pins, its overrides and its mods. Modrinth .mrpack and CurseForge .zip both work:

mlrc instance import Fabulously.Optimized.mrpack
mlrc launch --instance Fabulously-Optimized

CurseForge is a second source. It needs your own key and answers by project id:

mlrc config set general.curseforge_api_key <key>      # or export MLRC_CURSEFORGE_KEY
mlrc mod install 238222 --source curseforge    # Just Enough Items

Identity. Offline by default, under the name you pick:

mlrc config set auth.player_name Steve        # or `mlrc launch --username Steve`

Or sign in to a third-party Yggdrasil server, which adds skins and access to that service's online-mode servers. The password is asked for and never stored:

mlrc auth login --server https://littleskin.cn/api/yggdrasil --username [email protected]
mlrc auth accounts                                        # list, * marks the default
mlrc auth use <label>                                     # choose the default account
mlrc auth status

Tuning. Heap, language and download source, per run or remembered:

mlrc launch --memory 6G
mlrc config set java.xmx 6G
mlrc launch --lang zh_cn
mlrc config set launch.game_language zh_cn
mlrc --mirror bmclapi install 1.12.2           # auto probes both and remembers

Launch settings. JVM flags, game arguments, a command to run first, and the brand text the game shows in its corner - globally or per instance. ${...} markers work here exactly as they do in a version document:

mlrc config set launch.jvm_args "-XX:+UseG1GC -Dhere=${game_directory}"
mlrc config set launch.game_args "--demo"
mlrc config set launch.pre_launch "echo starting"
mlrc config set launch.brand "My Launcher"
mlrc instance create demo --version 1.21.1 --game-arg --demo --brand Demo
mlrc config set launch.jvm_args "-XX:+UseG1GC" --instance demo   # that instance only
mlrc config list --instance demo                                  # [instance] or [global], per key

Commands

Command	Purpose
mlrc install <version>	Install a version; --list lists what can be installed (--type, --limit), --loader fabric|quilt|forge|neoforge, --java=auto|install|skip, --dry-run, --threads N, --yes
mlrc launch [<version>]	Start the game; --instance <name>, --memory 4G, --jvm-arg <arg>, --lang <code>, --dry-run, --username, --width/--height, -- <args>
mlrc list [--all]	Installed versions, or every version in the manifest
mlrc use <version>	Set the default version
mlrc uninstall <version>	Remove a version; the shared cache is kept
mlrc instance create | list | remove	Instances: a version with its own worlds and mods, sharing the parent's files (--memory, --jvm-arg, --game-arg, --pre-launch, --brand)
mlrc mod search | install | list | update | remove | enable | disable	Mods from Modrinth (or CurseForge with --source curseforge), filtered by the version's loader and Minecraft version; installs bring their required dependencies, --dry-run shows them first
mlrc pack search | install | list | remove	Resource packs, shader packs and data packs; the kind is read from Modrinth, --world puts a data pack inside one world
mlrc instance import <pack>	Install a modpack (.mrpack or CurseForge .zip) as a new instance; --dry-run shows its contents first
mlrc java list | install | remove	Manage Java runtimes by major version or component
mlrc auth login | logout | status	Sign in to a Yggdrasil server, forget it, or show it
mlrc config get | set | list	Read or write config.toml; --instance <name> reads or writes an instance's layer (launch.* only)
mlrc cache prune [--keep-days N]	Drop cache objects nothing references
mlrc doctor	Check the data directory, network, runtimes and versions

Global flags: --data-dir, --json, --quiet, -v, --mirror.

Configuration

MLRC/config.toml:

[java]
custom = false      # true: honour java.path, JAVA_HOME and PATH
path = ""           # explicit java binary
xms = ""            # initial heap; empty leaves the JVM default
xmx = "2G"          # maximum heap; --memory and an instance's own value override it

[general]
default_version = ""
mirror = "auto"     # auto | official | bmclapi
proxy = "auto"      # auto | none | host:port; also passed to the game's JVM
game_language = ""  # e.g. zh_cn

[launch]
brand = ""               # corner text instead of MLRC; empty restores it
jvm_args = []            # e.g. ["-XX:+UseG1GC"]
game_args = []           # e.g. ["--demo"]
pre_launch = ""          # shell command, run in the game directory

[auth]
kind = "auto"            # auto | offline | yggdrasil | nide8
server = ""              # Yggdrasil API root; empty means offline only
player_name = "Player"   # offline name

An instance may override any of the launch values; an empty field inherits the global one.

Exit codes are stable: 0 success, 2 usage, 3 network, 4 authentication, 5 Java, 7 portable directory not writable, 8 version not installed. --json emits NDJSON events carrying the same error codes.

How it works

• Portable by default. Everything lives next to the executable: .minecraft for the standard layout, MLRC for the launcher's own data. If the folder is not writable the launcher fails with E_PORTABLE_READONLY instead of relocating into the user profile.
• Hashes are the authority. Every file is checked against the hash its source publishes (SHA1 from Mojang, SHA512 from Modrinth, SHA256 from the injector API), or against its length when a source publishes no hash. A mirror is only a URL substitution; a file it does not carry falls back to the official URL.
• Java is pinned per version. Runtimes live under MLRC/java/jdk-<major>/ and the host JDK is ignored unless java.custom=true, so a system JDK upgrade cannot break an installed version.
• An engine and a CLI. mlrc-core never prints and emits events; the CLI renders them as text or NDJSON.

Project layout

crates/
|-- mlrc-core/    engine: metadata, rules, downloads, store, java, launch
`-- mlrc-cli/     binary: argument parsing, rendering, prompts, exit codes

docs/DOCS.md is the design and the reasoning behind it, docs/DEVELOPMENT.md covers how the code is organised, and docs/API.md is the contract a front-end may depend on. CHANGELOG.md records what changed in each release; the release workflow publishes the matching section as the release notes.

Mirrors and attribution

The mirror support targets BMCLAPI. Its terms ask launchers to name the source in their download interface, so MLRC prints download source: BMCLAPI (...) and emits a source event when a download goes through it.

Legal

Not affiliated with Mojang or Microsoft. MLRC bundles no game files; it downloads them only when asked, and having a legitimate copy of Minecraft is still required to play on servers that verify ownership.

License

Apache-2.0, see LICENSE.