Adding a basic item is one of the first steps in modding. You're going to need to create an Item object, register it, and give it a texture. To add additional behavior to the item you will need a custom Item class. In this tutorial and all future ones, the “tutorial” namespace is used as a placeholder. If you have a separate mod id, feel free to use it instead.

First, create an instance of Item. The constructor takes in an Item.Settings (or a FabricItemSettings unless versions since 1.20.5) instance, which is used to set item properties such as the durability, and stack count. For simplicity, we just do it in ExampleMod class, and store them in static fields.

public class ExampleMod implements ModInitializer {
 
    // an instance of our new item
    // for versions below 1.20.4
    public static final Item CUSTOM_ITEM = new Item(new FabricItemSettings());
    // for versions since 1.20.5
    public static final Item CUSTOM_ITEM = new Item(new Item.Settings());
    [...]
}

We've create a basic item, but it still does not exist in Minecraft, because it has not been registered. In Minecraft, almost everything has an registry, and items are no exceptions.

You'll use the vanilla registry system for registering new content. The basic syntax is Registry.register(Registry Type, Identifier, Content). Registry types are stored as static fields in the Registries or Registry class, and the identifier is what labels your content. Content is an instance of whatever you're adding. Specifically for item, the syntax is Registry#register(Registries.ITEM, Identifier, Item). This can be called anywhere as long as it occurs during initialization. The method itself also returns the registered content itself.

For versions since 1.21, an Identifier is created through Identifier.of("namespace", "path"). For versions below 1.21, it is created through new Identifier("namespace", "path") or new Identifier("namespace:path"). It will fail if the namespace or path contains illegal characters.

public class ExampleMod implements ModInitializer {
 
    // an instance of our new item
    public static final Item CUSTOM_ITEM = new Item(new Item.Settings());
 
    @Override
    public void onInitialize() {
        // For versions below 1.21, please replace ''Identifier.of'' with ''new Identifier''
        Registry.register(Registries.ITEM, Identifier.of("tutorial", "custom_item"), CUSTOM_ITEM);
    }
}

For more simplicity, you can simplify your code by directly registering them when assigning the fields, as Register.register will also return the registered object:

public class ExampleMod implements ModInitializer {
 
    // an instance of our new item
    public static final Item CUSTOM_ITEM =
      // For versions below 1.21, use ''new Identifier("tutorial", "custom_item")''.
      Registry.register(Registries.ITEM, Identifier.of("tutorial", "custom_item"),
        new Item(new Item.Settings()));
 
    @Override
    public void onInitialize() {
    }
}

In the code above, you simply created one item. However, it is not convenient if you have many items in your mod, as you need to register and create an Identifier instance each time. Therefore, we can create a specific class to store item objects, such as ModItems or TutorialItems, and write a simple register method to conveniently register items. This is quite common in actual mod development. You may also check vanilla Items class to see how Minecraft completes it in a similar way.

In this example, create a TutorialItems class and refer to the class in the ModInitializer.

public final class TutorialItems {
 
    private TutorialItems() {}
 
    // an instance of our new item
    public static final Item CUSTOM_ITEM = register(new Item(new Item.Settings()), "custom_item");
 
    public static Item register(Item instance, String path) {
        // For versions below 1.21, please replace ''Identifier.of'' with ''new Identifier''
        return Registry.register(Registries.ITEM, Identifier.of("tutorial", path), instance);
    }
 
    public static void initialize() {
    }
}

Remember to refer to some method methods or fields in the mods initializes so as to statically load the class TutorialItems.

public class ExampleMod implements ModInitializer {
    @Override
    public void onInitialize() {
        TutorialItems.initialize();
    }
}

Note: Some experienced users may decide to use reflection to automatically register all static fields of a class. This is also a preferable way, but should be used with caution.

If you registered your item properly in the first step, you can successfully get your item by typing command /give @s tutorial:custom_item. You will find it has missing texture, and Minecraft will complain about a missing texture file in a fashion similar to this:

  [Server-Worker-1/WARN]: Unable to load model: 'tutorial:custom_item#inventory' referenced from: tutorial:custom_item#inventory: java.io.FileNotFoundException: tutorial:models/item/custom_item.json

That's because we haven't provided the item with textures and models. Therefore, you need to define the item model json and provide a texture image. You're going to need to add these to your resource directory. The direct path of each is:

• Item model: …/resources/assets/tutorial/models/item/custom_item.json
• Item texture: …/resources/assets/tutorial/textures/item/custom_item.png

Our example texture can be found here.

A basic item model template is:

{
  "parent": "item/generated",
  "textures": {
    "layer0": "tutorial:item/custom_item"
  }
}

The parent of your item model changes how it's rendered in the hand and comes in useful for things like block items in the inventory. item/generated is used for many simple items. item/handheld is used for tools that are held from the bottom left of the texture. In the json, textures/layer0 is the location of your image file.

You have created a simple item, and learned how to change some basic properties. But maybe you want it to have more behaviors. Therefore, you will need to create an item class. The default constructor requires an Item.Settings object.

public class CustomItem extends Item {
    public CustomItem(Settings settings) {
        super(settings);
    }
}

A practical use-case for a custom item class would be making the item play a sound when you use it:

public class CustomItem extends Item {
    public CustomItem(Settings settings) {
        super(settings);
    }
 
    @Override
    public TypedActionResult<ItemStack> use(World world, PlayerEntity user, Hand hand) {
        user.playSound(SoundEvents.BLOCK_WOOL_BREAK, 1.0F, 1.0F);
        return TypedActionResult.success(user.getStackInHand(hand));
    }
}

Replace the old Item object with an instance of your new item class:

public final class TutorialItems {
    [...]
 
    // an instance of our new item
    public static final CustomItem CUSTOM_ITEM = new CustomItem(new Item.Settings());
    [...]
}

For this you would use maxCount(int size) inside Item.Settings to specify the max stack size. Note that if your item is damageable you cannot specify a maximum stack size or the game will throw a RuntimeException.

public class ExampleMod implements ModInitializer {
 
    // An instance of our new item, where the maximum stack size is 16
    public static final CustomItem CUSTOM_ITEM = new CustomItem(new Item.Settings().maxCount(16));
    [...]
}

If you want to make it a fuel so that it can be used in a furnace, you can register in FuelRegistry when initializing the mod, for example:

public class ExampleMod implements ModInitializer {
    [...]
 
    @Override
    public void onInitialize() {
        [...]
        FuelRegistry.INSTANCE.add(TutorialItems.CUSTOM_ITEM, 300)
    }
}

In practice, when you have many items to register, as registering quantities of items may be effort-consuming and messy, you can consider placing them in a separate method. Here is an example:

public final class TutorialItems {
    [...]
 
    public static void registerFuels() {
        FuelRegistry.INSTANCE.add(CUSTOM_ITEM, 300)
    }
}

And then refer to this method in your ModInitializer:

public class ExampleMod implements ModInitializer {
    [...]
 
    @Override
    public void onInitialize() {
        [...]
        TutorialItems.registerFuels();
    }
}

Similarly, you can use a CompostingChanceRegistry to make it compostable in a composter.

Add your item to your own ItemGroup.