Lite Config

Lite Config is a JSON5/TOML configuration library for Minecraft mods on Fabric and NeoForge. Annotate any Java class with @Config and pass it to a builder to get a ConfigHolder that automatically manages file resolution, safe I/O, lifecycle events, sync, and more.

Features:

• Data layer: Handles JSON5/TOML formats, paths, default values, atomic writes, and automatic corruption recovery.
• State Management: Provides validated snapshots, deep copies, runtime updates, and custom state cloning.
• Opt-In Network Sync: Automatically synchronizes marked configs or individual fields from server to client.
• Async and Read-only: Offers synchronous, asynchronous, or read-only options to match your threading model.
• Restart Guards: Blocks runtime updates and defers synchronized changes for fields requiring a game restart.
• Custom Update API: update and updateAndSave return an UpdateResult with acceptance status and validation violations.
• Failure Policies: Granular control over read, write, and update errors, from graceful fallbacks to strict exceptions.
• Lifecycle Hooks: Event listeners for load, save, and update phases, plus config-level normalization and validation hooks.
• Declared constraints: Enforces numeric bounds, string patterns, and collection sizes, and more via annotations on load/update.
• Runtime Metadata: Access every field's path, type, default, comment, translation key, and constraints at runtime.
• Version Migrations: Uses stamped file revisions to upgrade older configs step-by-step without losing player data.
• Persistence Control: Fully customize file paths, field names, automated comments, and ignored fields.

Outside Lite Config's Scope:

• Config Screen: Lite Config is a data-layer solution and doesn't render config screens by itself, allowing you to pair it with any UI library or custom screens.

Documentation: Wiki

Setup

Artifacts are published to Maven Central under the group com.gmalvestiti.minecraft, with one artifact per loader:

Maven versions include the Lite Config version and the Minecraft build target:

The examples below target the 1.21 build.

Fabric

repositories {
    mavenCentral()
}

dependencies {
    modImplementation 'com.gmalvestiti.minecraft:liteconfig-fabric:1.2.0-1.21'
}

Declare the dependency so the loader refuses to start without it:

{
  "depends": {
    "liteconfig": ">=1.2.0-1.21"
  }
}

NeoForge

repositories {
    mavenCentral()
}

dependencies {
    implementation 'com.gmalvestiti.minecraft:liteconfig-neoforge:1.2.0-1.21'
}

Declare the dependency in META-INF/neoforge.mods.toml:

[[dependencies.yourmodid]]
modId = "liteconfig"
type = "required"
versionRange = "[1.2.0,)"
ordering = "NONE"
side = "BOTH"

Quickstart

The builder creates either a mutable or read-only holder. Every holder exposes synchronous methods for calling-thread work and asynchronous methods backed by the shared config worker:

Declare the config class. Initialize persisted fields to their defaults and provide a public no-argument constructor:

@Config(name = "mymod") // format defaults to JSON5
public final class MyModConfig {
    public boolean showHints = true;
    public int hudScale = 2;
}

or for TOML:

@Config(name = "mymod", format = ConfigFormat.TOML)
public final class MyModConfig {
    public boolean showHints = true;
    public int hudScale = 2;
}

Create the holder once during mod initialization and keep it for the lifetime of the mod. create() resolves the file path, validates the model, loads any existing file (or writes the defaults if none exists), and validates the loaded state — the holder is ready to read immediately after it returns:

public final class MyMod implements ModInitializer {

    public static final ConfigHolder<MyModConfig> CONFIG = LiteConfig.holder(MyModConfig.class)
        .modId("mymod")
        .create();
}

Read through data(), mutate through update / updateAndSave:

if (MyMod.CONFIG.data().showHints) {
    // ...
}

MyMod.CONFIG.updateAndSave(config -> config.hudScale = 3);

That writes config/mymod.json5:

{
  "showHints": true,
  "hudScale": 3
}

Full Configuration Example

@Config(
    name = "mymodfile",
    path = "mymoddir1/mymoddir2",
    format = ConfigFormat.JSON5,
    comment = "MyMod settings.",
    version = 3,
    stateCloner = MyModConfigCloner.class,
    readFailurePolicy = FailurePolicy.FALLBACK,
    writeFailurePolicy = FailurePolicy.STRICT,
    updateFailurePolicy = FailurePolicy.FALLBACK
)
public final class MyModConfig implements ConfigExtension {

    @Entry(
        name = "hud_scale",
        comment = "Scale of the HUD, from 1 to 4.",
        translationKey = "mymod.config.hud_scale",
        sync = true,
        callback = "onHudScaleChanged"
    )
    @Range(min = 1, max = 4)
    public int hudScale = 2;

    @Entry(comment = "Rendering backend. Applied after the next restart.", restart = true)
    public Renderer renderer = Renderer.DEFAULT;

    @AllowedValues({"mysql", "sqlite"})
    public String database = "sqlite";

    @Entry(comment = {"Profile used by server rules.", "Must be lowercase, alphanumeric, or underscore."})
    @Pattern("[a-z0-9_]+")
    @Length(max = 16)
    public String profileName = "default";

    @Entry(comment = "Server-owned spawn range.", sync = true)
    public IntRange spawnRange = new IntRange(1, 12);

    public Display display = new Display();

    @Ignore
    public Map<String, String> runtimeCache = new HashMap<>();

    @Override
    public void afterLoad() {
        if (profileName != null) {
            profileName = profileName.strip().toLowerCase(Locale.ROOT);
        }
    }

    @Override
    public void beforeSave() {
        if (display != null && display.hiddenHints != null) {
            display.hiddenHints.sort(String::compareTo);
        }
    }

    @Override
    public void validate(List<Violation> violations) {
        if (spawnRange == null || spawnRange.minimum() > spawnRange.maximum()) {
            violations.add(Violation.of(
                "spawn-range.order",
                "spawnRange minimum must not exceed its maximum"
            ));
        }
    }

    private void onHudScaleChanged(Integer oldValue, Integer newValue, boolean fromSync) {
        System.out.printf("HUD scale: %d -> %d (from server: %s)%n",
            oldValue, newValue, fromSync);
    }

    @Migration(from = 1)
    static void toVersion2(ConfigData data) {
        data.rename("hudScale", "hud_scale");
    }

    @Migration(from = 2)
    static void toVersion3(ConfigData data) {
        if (!data.has("spawnRange")) {
            data.set("spawnRange.minimum", 1)
                .set("spawnRange.maximum", 12);
        }
    }

    public static final class Display {
        @Entry(comment = "Show contextual hints.")
        public boolean showHints = true;

        @Length(max = 32)
        public List<String> hiddenHints = new ArrayList<>();
    }

    public enum Renderer {
        DEFAULT,
        COMPATIBILITY
    }
}

// Custom type
public record IntRange(int minimum, int maximum) {
    public static final Codec<IntRange> CODEC = RecordCodecBuilder.create(instance ->
        instance.group(
            Codec.INT.fieldOf("minimum").forGetter(IntRange::minimum),
            Codec.INT.fieldOf("maximum").forGetter(IntRange::maximum)
        ).apply(instance, IntRange::new)
    );

    public static final StreamCodec<ByteBuf, IntRange> STREAM_CODEC =
        StreamCodec.composite(
            ByteBufCodecs.VAR_INT, IntRange::minimum,
            ByteBufCodecs.VAR_INT, IntRange::maximum,
            IntRange::new
        );
}

// Custom config state cloner
public static final class Cloner implements StateCloner<MyModConfig> {
    @Override
    public MyModConfig copy(MyModConfig source) {
        MyModConfig copy = new MyModConfig();
        copy.hudScale = source.hudScale;
        copy.renderer = source.renderer;
        copy.profileName = source.profileName;
        copy.spawnRange = source.spawnRange;
        copy.display = copyDisplay(source.display);
        copy.runtimeCache = source.runtimeCache == null
            ? new HashMap<>()
            : new HashMap<>(source.runtimeCache);
        return copy;
    }

    private static Display copyDisplay(Display source) {
        if (source == null) {
            return null;
        }
        Display copy = new Display();
        copy.showHints = source.showHints;
        copy.hiddenHints = source.hiddenHints == null
            ? null
            : new ArrayList<>(source.hiddenHints);
        return copy;
    }
}

Register custom codecs while creating a holder. Registrations use the shared process-wide registry and are not bound to that holder or config. The Codec controls JSON5/TOML persistence and state copying; if it rejects a value, Lite Config falls back to reflective serialization for that use. The StreamCodec controls synchronization. Lite Config's loader entrypoints handle the packets, handshake, batching, and server broadcasts.

public final class MyMod implements ModInitializer {

    public static ConfigHolder<MyModConfig> config = LiteConfig.holder(MyModConfig.class, codecs -> codecs
            .registerCodec(IntRange.class, IntRange.CODEC)
            .registerStreamCodec(IntRange.class, IntRange.STREAM_CODEC))
        .modId("mymod")
        .onLoad(ConfigSide.SERVER, state -> System.out.println("Loaded profile " + state.profileName))
        .onUpdate(ConfigSide.BOTH, state -> System.out.println("HUD scale is now " + state.hudScale))
        .onSave(ConfigSide.SERVER, state -> System.out.println("Saved MyMod config"))
        .create();

    @Override
    public void onInitialize() {
        // As an alternative to the holder's codec registration above
        LiteConfig.codecs()
            .registerCodec(IntRange.class, IntRange.CODEC)
            .registerStreamCodec(IntRange.class, IntRange.STREAM_CODEC);

        // Fast shared read. Treat the returned object as read-only.
        int currentScale = config.data().hudScale;

        // Stable deep copy owned by this caller.
        MyModConfig snapshot = config.copy();
        snapshot.display.hiddenHints.add("crafting");

        // Validated in-memory update.
        UpdateResult result = config.update(state -> {
            state.hudScale = 3;
            state.display.hiddenHints = new ArrayList<>(
                snapshot.display.hiddenHints
            );
        });
        if (!result.accepted()) {
            result.violations().forEach(violation ->
                System.err.println(violation.id() + ": " + violation.message()));
        }

        // Serialized update and save. Synced values are broadcast by the server after acceptance.
        config.updateAndSaveAsync(state ->
            state.spawnRange = new IntRange(2, 24)
        ).thenAccept(update ->
            System.out.println("Saved: " + update.accepted()));

        // Structural metadata for screens, commands, generated help, etc.
        config.metadata().flatten().forEach(property ->
            System.out.println(property.path() + " -> " + property.type().getSimpleName()));
    }
}

The first create() loads config/mymoddir1/mymoddir2/mymodfile.json5, migrates older revisions in order, validates the result, and writes the accepted state back. A file without configVersion starts at version 1. Only hud_scale and spawnRange are synchronized because they opt in with sync = true; the other values remain local. Use @Config(sync = true) instead when every persisted leaf is server-owned.