View source for Minecraft:Java Edition client command line arguments

<noinclude>{{italic title|Java Edition}}
When starting the ''[[Minecraft:Java Edition]]'' [[Minecraft:client.jar|client]], the ''[[Minecraft:Minecraft Launcher]]'' passes various '''command line arguments''' to the {{wp|Java virtual machine}}, such as the path to the game itself and account login information. These arguments are chosen based on the contents of the {{mono|[[Minecraft:client.json]]}} file corresponding to the selected version, options set in the launcher, and the current operating system.

== Command line parts ==

The complete command line used to start the JVM consists of the following parts:

* Location of the JVM executable. Defaults either to a JVM provided by the system, or a JVM automatically downloaded by the launcher. May be changed in [[Minecraft:Minecraft Launcher#Installations|installation options]] in the launcher.
* Arguments to configure the JVM, such as {{code|-cp}} (classpath) to specify the locations of required libraries and the main {{mono|client.jar}}. Generated based on {{code|arguments.jvm}} in {{mono|[[Minecraft:client.json]]}}.
* Additional JVM arguments specified in [[Minecraft:Minecraft Launcher#Installations|installation options]] in the launcher.
* Name of the main class. Specified as {{code|mainClass}} in {{mono|[[Minecraft:client.json]]}}.
* Arguments to the game itself, such as {{code|--gameDir}} to specify the base directory for user-generated game files. Generated based on {{code|arguments.game}} in {{mono|[[Minecraft:client.json]]}}.
* Additional game arguments specified in [[Minecraft:Minecraft Launcher#Installations|installation options]] in the launcher.

== JVM arguments ==
{| class="wikitable"
|- 
! Argument
! Description
|-
| {{code|-Djava.library.path{{=}}{{ph|natives folder}}}}
| The path to the native libraries.
|-
| {{code|-cp {{ph|jars}}}}
| The absolute paths listing the game and library jars to load, separated by {{code|;}} on Windows or {{code|:}} on Linux and macOS.
|-
| {{code|-Dminecraft.launcher.brand{{=}}{{ph|launcher name}}}}
| The name of the launcher.{{info needed|What does the game use this information for?}}
|-
| {{code|-Dminecraft.launcher.version{{=}}{{ph|launcher version}}}}
| The version of the launcher.{{info needed|What does the game use this information for?}}
|-
| {{code|-Dos.name{{=}}Windows 10 -Dos.version{{=}}10.0}}
| Tells Java to state that it is running on Windows 10 even when it's not.{{info needed|Why and when is this used?}}
|-
| {{code|-XX:HeapDumpPath{{=}}MojangTricksIntelDriversForPerformance_javaw.exe_minecraft.exe.heapdump}}
| Supposedly makes Intel drivers on laptops with two GPUs use the dedicated GPU.<ref>{{reddit|d8j90e|comment/f1b2anr|apparently Intel drivers on laptops with two graphics cards scan the process name for strings like "minecraft" and "javaw.exe" and switch to the dedicated GPU if it sees those names.|scratchisthebest|September 24, 2019}}</ref>
|-
| {{code|-XstartOnFirstThread}}
| Tells the JVM to start on the first thread.<br>Some macOS versions require this while others break with it, leaving the game stuck as "not responding".
|-
| {{code|-Xss1M}}
| Sets the per thread stack size to 1 MB.
|}

== Game arguments ==
{| class="wikitable"
|- 
! Argument
! Description
|-
| {{code|--clientId {{ph|client ID}}}}
| The optional base64 encoded [[Minecraft:UUID]] from {{file|file|clientId.txt}} in [[Minecraft:.minecraft]] used for [[Minecraft:telemetry]]. The file is generated by the launcher if it's missing.
|-
| {{code|--username {{ph|player name}}}}
| The player's name used for offline mode.{{info needed|Is it used in online mode?}}
|-
| {{code|--uuid {{ph|UUID}}}}
| The player's UUID.
|-
| {{code|--xuid {{ph|XUID}}}}
| The Xbox User ID.
|-
| {{code|--userType {{ph|authentication scheme}}}}
| The authentication scheme used for logging in.
{{code|msa}} for [[Minecraft:Microsoft authentication]]<br>
{{code|mojang}} for [[Minecraft:Yggdrasil|Yggdrasil (Legacy Mojang authentication)]]<br>
{{code|legacy}} for [[Minecraft:Legacy Minecraft authentication]]
|-
| {{code|--accessToken {{ph|access token}}}}
| The token generated during the login, required for joining servers. The format depends on the authentication scheme.
|-
| {{code|--demo}}
| Switches the game to [[Minecraft:Demo Mode]].
|-
| {{code|--version {{ph|version name}}}}
| The name of the version. Specified in [[Minecraft:client.json]] and [[Minecraft:version_manifest.json]] under {{code|id}}. Shown in the [[Minecraft:debug screen]] and in crash reports.
|-
| {{code|--versionType {{ph|version type}}}}
| The type of the version. Usually {{code|release}}, {{code|snapshot}}, {{code|old_beta}} or {{code|old_alpha}}, specified in [[Minecraft:client.json]] and [[Minecraft:version_manifest.json]] under {{code|type}}. Shown in the [[Minecraft:debug screen]] and in crash reports. 
|-
| {{code|--gameDir {{ph|game folder}}}}
| The folder for the instance's files. {{file|directory|[[Minecraft:.minecraft]]}} by default.
|-
| {{code|--assetsDir {{ph|assets folder}}}}
| The folder that contains, among others, the {{file|directory|objects}} folder. {{file|directory|[[Minecraft:.minecraft]]/assets}} by default.
|- 
| {{code|--assetIndex {{ph|assets index name}}}}
| The JSON file for mapping internal names to indexes into the {{file|directory|assets/objects}} folder. {{file|directory|[[Minecraft:.minecraft]]/assets/indexes/{{ph|version}}.json}} by default.
|-
| {{code|--width {{ph|width}}}}
| The initial width of the game's window.
|-
| {{code|--height {{ph|height}}}}
| The initial height of the game's window.
|-
| {{code|--disableMultiplayer}}
| Disables the multiplayer button.
|-
| {{code|--disableChat}}
| Disables sending and receiving chat messages.
|-
| {{code|--quickPlayPath {{ph|quick play logs path}}}}
| The optional path from the [[Minecraft:.minecraft]] folder to the [[Minecraft:quick play]] logs file.
|-
| {{code|--quickPlaySingleplayer {{ph|world name}}}}
| The optional name of the world to automatically join once the game has started.
|-
| {{code|--quickPlayMultiplayer {{ph|server address}}}}
| The optional address of a server to automatically join once the game has started.
|-
| {{code|--quickPlayRealms {{ph|realm ID}}}}
| The optional ID of a realm to automatically join once the game has started.
|}

== Legacy arguments ==
{| class="wikitable"
|- 
! Argument
! Description
! Versions
|-
| {{code|--tweakClass {{ph|tweaker class}}}}
| An optional class implementing {{code|net.minecraft.launchwrapper.ITweaker}} that can modify other classes while the game is starting.
The vanilla tweakers are in the {{code|net.minecraft.launchwrapper}} package, for example {{code|net.minecraft.launchwrapper.VanillaTweaker}}.
| presumable at least Indev to Alpha{{info needed|Which versions had these arguments?}}
|-
| {{code|--session {{ph|session authentication}}}}
| The session ID used to authenticate with Mojang while connecting to servers.
Defined as: {{code|token:{{ph|access authentication token}}:{{ph|authentication UUID}}}}.
| rowspan=3 | unknown{{info needed|Which versions had these arguments?}}
|-
| {{code|--userProperties {{ph|user properties}}}}
|  unknown{{info needed|What did it do?}}
|-
| {{code|--server {{ph|server address}}}}
| The same as the new {{code|--quickPlayMultiplayer {{ph|server address}}}}.
|-
| {{code|--workDir {{ph|game folder}}}}
| The same as the new {{code|--gameDir {{ph|game folder}}}}.
| 13w16a to 13w23b
|-
| {{code|--assetsDir {{ph|assets folder}}}}
| The assets folder, presumably {{file|directory|[[Minecraft:.minecraft]]/assets/virtual/legacy}}.{{info needed|How did it differ from --assetsDir?}}
| until 13w48b
|}

== Main class ==

A versions default main class is in it's [[Minecraft:version.json]] under {{code|mainClass}}.

{| class="wikitable"
|- 
! Class
! colspan=2 | Versions
|-
| {{code|net.minecraft.client.main.Main}}
| colspan=2 | after 1.5.2
|-
| {{code|net.minecraft.launchwrapper.Launch}}
| rowspan=2 | Alpha 1.0.11 to 1.5.2
| new launcher
|-
| {{code|net.minecraft.client.Minecraft}}
| old launcher
|-
| {{code|{{ph|obfuscated}}}}
| start of Alpha to Alpha 1.0.5_01
| launcher 
|-
| {{code|net.minecraft.client.MinecraftApplet}}
| Alpha
| website applet
|-
| {{code|net.minecraft.minecraft.{{ph|obfuscated}}}}
| rowspan=2 | Indev and Infdev
| launcher 
|-
| {{code|net.minecraft.client.MinecraftApplet}}
| website applet
|-
| {{code|com.mojang.minecraft.{{ph|obfuscated}}}}
| Classic 0.0.13a_03 to end of Classic
| rowspan=2 | launcher 
|-
| {{code|com.mojang.minecraft.Minecraft}}
| start of Classic to Classic 0.0.13a
|-
| {{code|com.mojang.minecraft.MinecraftApplet}}
| Classic
| website applet
|-
| {{code|com.mojang.minecraft.RubyDung}}
| colspan=2 | late pre-Classic
|-
| {{code|com.mojang.rubydung.RubyDung}}
| colspan=2 | early pre-Classic
|}

== Assets ==
{{main article|Minecraft Wiki:Projects/wiki.vg merge/Game files#Assets}}

The launcher downloads additional required resources and saves them to {{file|directory|[[Minecraft:.minecraft]]/assets}} to be used by the game.

Minecraft requires several arguments when launched.

Since 1.12.2, they are defined in [[Minecraft:client.json]] under {{code|arguments}}.

Before that, the game arguments were defined in [[Minecraft:client.json]] under {{code|minecraftArguments}} while the JVM arguments were defined directly in the launcher.

== References ==
{{reflist}}

[[Category:Java Edition protocol]]