Creating Plugins [1.13 and Up]

Creating a JEI Plugin

Now that you're done with gradle in Getting Started, it's time to create your plugin.

JEI plugins implement the IModPlugin and are annotated with @JeiPlugin.

Under Forge, JEI uses the @JeiPlugin annotation to find your mod plugin class, and then creates an instance at runtime.

Under Fabric, JEI uses fabric.mod.json entrypoints. Add your plugin's location to a "jei_mod_plugin" entrypoint. In this example, three plugins are added:

  "entrypoints": {
    "main": [
      "mezz.jei.fabric.JustEnoughItems"
    ],
    "client": [
      "mezz.jei.fabric.JustEnoughItemsClient"
    ],
    "jei_mod_plugin": [
      "mezz.jei.common.plugins.vanilla.VanillaPlugin",
      "mezz.jei.common.plugins.jei.JeiInternalPlugin",
      "mezz.jei.common.plugins.debug.JeiDebugPlugin"
    ]
  },

Loading this way has the advantage that you can keep all references to JEI in your plugin, separate from your other code.
The plugin code will only get called when JEI is there, so it will never crash from missing classes.

Implementation

Plugins are broken into many stages, each with a specific purpose. Although there are many stages to a JEI plugin, not all of them are necessarily needed for your plugin!

registerItemSubtypes

This is where plugins tell JEI how to handle items that have subtypes that depend on NBT or capabilities instead of meta.
See the page on Item Subtypes.

registerIngredients

This is an advanced section where plugins tell JEI about ingredients.
The Vanilla plugin registers ItemStack and FluidStack as ingredients here.
Just about anything can be an ingredient. To add your own, see Non-Item Ingredients (WARNING, link not for 1.13 and up!).

registerCategories

This is where plugins tell JEI about custom recipe categories.
The Vanilla plugin uses this to register all of the Vanilla crafting categories (regular crafting, smelting, etc.)

registerVanillaCategoryExtensions

This is where plugins can tell JEI about any extensions to pre-existing Vanilla categories.

registerRecipes

This is where recipes for any recipe categories (whether modded or vanilla) are registered.
More precisely, this is where you should register any custom recipes that JEI does not automatically handle (custom machine recipes, etc.).

registerRecipeTransferHandlers

This is where you should register any custom transfer handlers.
Put simply, a transfer handler is what allows the + button in JEI to transfer items to the appropriate slots.

registerRecipeCatalysts

This is where you should register any items that are used to craft recipes.
For example, if your mod introduces a custom machine that has its own recipes, you should register your machine here to be the catalyst in making said recipes.