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Version: 1.20.4


Configurations define settings and consumer preferences that can be applied to a mod instance. NeoForge uses a configuration system using TOML files and read with NightConfig.

Creating a Configuration

A configuration can be created using a subtype of IConfigSpec. NeoForge implements the type via ModConfigSpec and enables its construction through ModConfigSpec.Builder. The builder can separate the config values into sections via Builder#push to create a section and Builder#pop to leave a section. Afterwards, the configuration can be built using one of two methods:

buildCreates the ModConfigSpec.
configureCreates a pair of the class holding the config values and the ModConfigSpec.

ModConfigSpec.Builder#configure is typically used with a static block and a class that takes in ModConfigSpec.Builder as part of its constructor to attach and hold the values:

// In some config class
ExampleConfig(ModConfigSpec.Builder builder) {
// Define values here in final fields

// Somewhere the constructor is accessible
static {
Pair<ExampleConfig, ModConfigSpec> pair = new ModConfigSpec.Builder()
// Store pair values in some constant field

Each config value can be supplied with additional context to provide additional behavior. Contexts must be defined before the config value is fully built:

commentProvides a description of what the config value does. Can provide multiple strings for a multiline comment.
translationProvides a translation key for the name of the config value.
worldRestartThe world must be restarted before the config value can be changed.


Config values can be built with the provided contexts (if defined) using any of the #define methods.

All config value methods take in at least two components:

  • A path representing the name of the variable: a . separated string representing the sections the config value is in
  • The default value when no valid configuration is present

The ConfigValue specific methods take in two additional components:

  • A validator to make sure the deserialized object is valid
  • A class representing the data type of the config value
// For some ModConfigSpec.Builder builder
ConfigValue<T> value = builder.comment("Comment")
.define("config_value_name", defaultValue);

The values themselves can be obtained using ConfigValue#get. The values are additionally cached to prevent multiple readings from files.

Additional Config Value Types

  • Range Values
    • Description: Value must be between the defined bounds
    • Class Type: Comparable<T>
    • Method Name: #defineInRange
    • Additional Components:
      • The minimum and maximum the config value may be
      • A class representing the data type of the config value

DoubleValues, IntValues, and LongValues are range values which specify the class as Double, Integer, and Long respectively.

  • Whitelisted Values

    • Description: Value must be in supplied collection
    • Class Type: T
    • Method Name: #defineInList
    • Additional Components:
      • A collection of the allowed values the configuration can be
  • List Values

    • Description: Value is a list of entries
    • Class Type: List<T>
    • Method Name: #defineList, #defineListAllowEmpty if list can be empty
    • Additional Components:
      • A validator to make sure a deserialized element from the list is valid
  • Enum Values

    • Description: An enum value in the supplied collection
    • Class Type: Enum<T>
    • Method Name: #defineEnum
    • Additional Components:
      • A getter to convert a string or integer into an enum
      • A collection of the allowed values the configuration can be
  • Boolean Values

    • Description: A boolean value
    • Class Type: Boolean
    • Method Name: #define

Registering a Configuration

Once a ModConfigSpec has been built, it must be registered to allow NeoForge to load, track, and sync the configuration settings as required. Configurations should be registered in the mod constructor via ModLoadingContext#registerConfig. A configuration can be registered with a given type representing the side the config belongs to, the ModConfigSpec, and optionally a specific file name for the configuration.

// In the mod constructor with a ModConfigSpec CONFIG
ModLoadingContext.get().registerConfig(Type.COMMON, CONFIG);

Here is a list of the available configuration types:

TypeLoadedSynced to ClientClient LocationServer LocationDefault File Suffix
CLIENTClient Side OnlyNo.minecraft/configN/A-client
COMMONOn Both SidesNo.minecraft/config<server_folder>/config-common
SERVERServer Side OnlyYes.minecraft/saves/<level_name>/serverconfig<server_folder>/world/serverconfig-server

NeoForge documents the config types within their codebase.

Configuration Events

Operations that occur whenever a config is loaded or reloaded can be done using the ModConfigEvent.Loading and ModConfigEvent.Reloading events. The events must be registered to the mod event bus.


These events are called for all configurations for the mod; the ModConfig object provided should be used to denote which configuration is being loaded or reloaded.