Proper Mod Structuring

The structure of your mod is important in keeping your mod organized, for both your benefit and the benefit of anyone who wishses to make a feature for your mod. A disorganized mod structure may cause headaches when someone is trying to update it to a higher version, especially if they cannot modify the package structure, due to i.e. licensing.

Note that this page is only a recommendation for your mod structure; you may structure your mod in any way you see fit.

Packaging

Pick a unique package name for your mod. If you own a URL associated with your project, you can use it as your top level package. For example if you own "example.com", you may use com.example as your top level package. The next level package is usually your mod's ID: if your mod ID is examplemod, your mod's package will be com.example.examplemod.

Important

Do not use a domain for your top level package if you do not own that domain. It is perfectly acceptable to have your top level package be named with anything, such as your name/nickname, or the name of the mod (me.exampledude.examplemod).

Using Subpackages

Rather than clutter up a single class and package with everything, it is recommended you break your mod into subpackages. Below are a few possible methods for laying out your folder structure though you may as well come up with your own layout too.

Group by Logic: One possible strategy is to make subpackages for logical units of your mod. For example, if you have a block called Super Furnace you would put its block, its block entity and its item all under feature/superfurnace.
Group by Function: Another common strategy is to make subpackages for grouping classes that have a common purpose. For example, your blocks classes can be under blocks, your entities classes can be under entities, your helper utilities can be under helpers, etc.

No matter how your final structure looks like it is highly recommended to add a client subpackage under your main package. This helps to isolate your client-only code from the rest, such as your Screens and renderers.

By keeping your code in clean subpackages, you can grow your mod much more organically.

If you are unsure on how exactly you want to structure your mod it can be a good idea to look at the source of others to see how they did it.

Class Naming Schemes

A common class naming scheme allows easier deciphering of the purpose of the class, and makes it easier for someone developing for your mod to find specific classes.

The usual style is to use suffixes for your classes, for example:

An Item called PowerRing would have a class name of PowerRingItem.
A Block called NotDirt would have a class name of NotDirtBlock.
A BlockEntity for a block called SuperChewer would have a class name of SuperChewerBlockEntity.

The Mod File

The main mod class - the class that is annotated with @Mod - is usually put into the main package of your mod, and not placed into a subpackage. This allows an easier time to access this, as your main mod class is the entrypoint of your mod.

The @Mod annotation indicates to the mod loader that this class is the entry point of your mod. Each @Mod annotation and their value should be paired with a mod id entry in your mods.toml file.

The `mods.toml` file

The mods.toml file is read by the mod loader to determine what mods are packaged into your JAR file, and what information to display to the user in the Mods listing screen (accessible by pressing the "Mods" button on the main menu of the game).

The mods.toml file is formatted in Tom's Obvious Minimal Language, or TOML for short. The example mods.toml file in the MDK provides comments explaining the contents of the file. It should be stored under the META-INF folder in your resources directory (src/main/resources/META-INF/mods.toml).

Example mods.toml file

modLoader="javafml"
# Forge for 1.17.1 is version 37
loaderVersion="[37,)"
license="All rights reserved"
issueTrackerURL="github.com/MinecraftForge/MinecraftForge/issues"
showAsResourcePack=false

[[mods]]
    modId="examplemod"
    version="1.0.0.0"
    displayName="Example Mod"
    updateJSONURL="minecraftforge.net/versions.json"
    displayURL="minecraftforge.net"
    logoFile="logo.png"
    credits="I'd like to thank my mother and father."
    authors="Author"
    description='''
Lets you craft dirt into diamonds. This is a traditional mod that has existed for eons. It is ancient. The holy Notch created it. Jeb rainbowfied it. Dinnerbone made it upside down. Etc.
    '''

[[dependencies.examplemod]]
    modId="forge"
    mandatory=true
    versionRange="[37,)"
    ordering="NONE"
    side="BOTH"

[[dependencies.examplemod]]
    modId="minecraft"
    mandatory=true
    versionRange="[1.17.1,1.18)"
    ordering="NONE"
    side="BOTH"

If the version is specified as${file.jarVersion}, Forge will replace the string with the 'Implementation Version' specified in the jar manifest at runtime. Since the userdev environment has no jar manifest to pull from, it will be NONE instead. As such, it is usually recommended to leave this field alone.

The mods.toml is split into three parts: the non-mod-specific properties, which are linked to the mod file; the mod properties, with a section for each mod; and dependency configurations, with a section for each mod's dependencies. Here is a table of attributes that may be given to a mod, wheremandatorymeans there is no default and the absence of the property causes an error.

Non-Mod-Specific Properties

Property	Type	Defaults	Description	Example
`modLoader`	string	mandatory	The language loader for the mod. Used to specify an alternative language for the mod, such as Kotlin, if one exists. The Forge-provided Java loader is `javafml`.	`"javafml"`
`loaderVersion`	string	mandatory	The acceptable version range of the language loader, expressed as a Maven version spec. For the Forge-provided Java loader, the version is the major version of the Forge version.	`"[37,)"`
`license`	string	mandatory	The license for the mod(s) in this JAR. This string may be any valid string, but it is suggested to set the value to be the name of your license, and/or a link to that license.	`"GNU GPL v3, https://www.gnu.org/licenses/gpl-3.0.en.html"`
`showAsResourcePack`	boolean	`false`	Whether to display this mod's resources as a separate option in the resource pack menu. If disabled, the mod's resources will be rolled into the "Mod resources" pack.	`true`
`properties`	table	`{}`	A table of custom substitution properties. This is used by `StringSubstitutor` to replace values, using `${file.*}`.	`{ "thingy" = 1 }`, used in `${file.thingy}`
`issueTrackerURL`	string	nothing	A URL for an issues tracker. This should never be a blank string, as that will cause an error.	`"http://my.issue.tracker/"`

Mod Properties

A mod entry is defined by a new section starting with a [[mods]] header (In TOML, the [[mods]] defines an array of tables). All properties from that line until the next header will become the properties for that mod.

Property	Type	Defaults	Description	Example
`modId`	string	mandatory	The mod's identifier (modid). This must match the following regex: `^[a-z][a-z0-9_-]{1,63}$` (starts with a lowercase letter; other characters must be a lowercase letter, number, underscore or hyphen; must be 2-64 characters long).	`"examplemod"`
`namespace`	string	value of `modId`	An override namespace. Currently, there is no use for this property	`example`
`version`	string	`"1"`	.), ideally conforming to [[Semantic_Versioning>Semantic Versioning]]. The default value in the MDK for this is `${file.jarVersion}`, which is replaced at runtime with the `Implementation-Version` found in the jar's manifest file.	`"0.2.4-beta1"`
`displayName`	string	value of `modId`	The display name of the mod, for use in the Mods listing screen	`"Example Mod"`
`description`	string	`"MISSING DESCRIPTION"`	The description of the mod, for use in the Mods listing screen. It's recommended to use a multiline string (surrounded by `)`	`"Adds things and stuff. "`
`logoFile`	string	nothing	The path of the logo file image, for use in the Mods listing screen. The image must be in the root of the jar file, not in any subfolder thereof (e.g. the file is directly in `src/main/resources`)	`"myAwesomeLogo.png"`
`logoBlur`	boolean	`true`	Whether to do some blurring on the mod's logo in the Mods listing screen. Has no effect if `logoFile` is not set.	`false`
`updateJSONURL`	string	nothing	The update JSON URL, used by the [Update_Checker update checker]. This should never be a blank string, as that will cause an error.	`"http://myurl.me/path/to/update.json"`
`modproperties`	table	`{}`	A table of custom mod properties; this is not used for Forge, but is mainly for use by mods.	`{ "useThing" = true }`
`credits`	string	nothing	Credits and acknowledgements for the mod, for use in the Mods listing screen. Can be any string.	`"This person and that guy"`
`authors`	string	nothing	Authors for the mod, for use in the Mods listing screen. Can be any string.	`"ExampleDude"`
`displayURL`	string	nothing	A URL, displayed on the Mods listing screen. Can be any string.	`"http://example.com/"`

Dependency Configurations

Mods can define dependencies for their mods, which are checked by Forge before loading mods. This is used for e.g. ensuring your mod loads after another, or hard-crashing if a mod with a specified version does not exist.

These dependency configurations, like the mod properties, are defined by a new section starting with dependencies., with being the mod id that has this dependency. All properties from that line until the next header will become the properties of that dependency configuration.

Property	Type	Defaults	Description	Example
`modId`	string	mandatory	The mod id of the dependency.	`examplelibrary`
`mandatory`	boolean	mandatory	Whether to crash if this dependency is not met.	`true`
`versionRange`	string	`""`	The acceptable version range of the dependency, expressed as a Maven version spec. An empty string is an unbounded version range, which matches any version.	`"[1.0,2.0)"`
`ordering`	string	`"NONE"`	Defines if the mod must load before or after this dependency. The valid values are `BEFORE` (must load before), `AFTER` (must load after), and `NONE` (does not care about order).	`"AFTER"`
`side`	string	`"BOTH"`	physical side]]. The valid values are `CLIENT` (present on the client), `SERVER` (present on the dedicated server), and `BOTH` (present on both sides).	`"CLIENT"`

Warning

When specifying dependency ordering between two or more mods, beware of cyclic order!

An example: if mod A must load before mod B, and mod B must load before mod A, the game will crash because of the circular cycle.