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Naming conventions


Use UpperCamelCase for class names. Use lowerCamelCase for method names, variable names, and names of fields that are not both static and final. Use UPPER_SNAKE_CASE for names of fields that are both static and final.

Method names should generally be verb phrases (tick, getCarversForStep), except for "withX", "toX", "fromX", "of" and builder methods. Class names and non-boolean field and variable names should be noun phrases (ChunkRegion, color). Boolean field and variable names should always be adjective phrases or present tense verb phrases (powered, canOpen), avoiding the is and has prefixes when possible (colored, not isColored or hasColor).

To make code as easy to read as possible, keep names in the natural language order. For example, a class representing a chest block entity should be named ChestBlockEntity rather than BlockEntityChest. Though prefix naming may be helpful for grouping classes together in an IDE's tree view, reading and writing code is done much more often than browsing files.


Use American English for consistency throughout Yarn and with known Mojang names.

If there are two acceptable spellings of the same word, first check if one is already being used in Yarn or by Mojang, and if not, use the most common spelling.


Omit words that are made redundant by parameter names or owner class names. For example, use getChunk(BlockPos pos) rather than getChunkAtPosition(BlockPos pos) and Box.create rather than Box.createBox. Don't avoid overloading methods or shadowing fields.

However, it's more important for a name to be descriptive rather than short, so don't omit important words. When naming something always look at all its usages, including overriding methods and inheriting classes.

It's important to be concise especially with names used in many places throughout the code, while more obscure names can be longer and more descriptive.


Avoid abbreviations unless it's a common one everyone knows and other yarn names involving the same word use its abbreviated form. Full names are easier to read quickly and remember ("Which words were abbreviated?") and they often don't take more time to type thanks to IDE autocompletion. Common abbreviations you should use are:

  • "id" for "identifier"
  • "pos" for "position"
  • "nbt" for "named binary tag"
  • "init" for "initialize"
  • "min"/"max" for "minimum"/"maximum"
  • Any abbreviations used by Java or libraries ("json", "html", etc.)
  • "o" for the parameter of equals(Ljava/lang/Object;)Z methods

Treat acronyms as single words rather than capitalizing every letter. This improves readability (compare JsonObject and JSONObject) and it's consistent with Mojang naming (a known name is NbtIo).


Package names should always be singular to respect Java conventions. Try to respect the Mojang package structure to avoid visibility problems in the future.


Consistency is important as it makes code more readable and names easier to memorize. When possible, use terms that are present in other Yarn names, in libraries used by Minecraft, or in vanilla strings. The rest of this section lists common names and name patterns you should use.

Ticks and updates

Use "tick" for updates done once per tick. Use "update" for other kind of updates.

Value last tick

Use the word "last" for the value that something had last tick (lastX, lastWidth, etc.).

Getters, setters, withers, and creators

Use "get" for non-boolean getters and other methods that calculate some property with no side effects other than caching a value in a private field. For boolean getters, use "is".

Use "set" for methods that set some property. Name the parameter the same as the property (setColor(color), not setColor(newColor)).

Use "with" for methods that return a copy of an object with a different value for some property. Name the parameter the same as the property.

Use "create" for methods that create a new instance of some object. Use "get or create" for methods that create a new instance only if one does not already exist. Don't use "get or create" for lazy initialization, though.


Use "serializer" for objects whose purpose is serializing or deserializing some type of object (RecipeSerializer). Use "serialize" and "deserialize" for methods only when serializing or deserializing an object other than the one the method is in.

Use "from" for static methods that create an object of the method owner's type (fromJson, fromNbt, fromString). Use "to" for methods that convert an object to another type (toString, toLong, toNbt).

Use "read" for non-static methods that load data into the object. Use "write" for methods that save data to an existing object passed as a parameter.

Factories and builders

Use "factory" for objects whose purpose is creating other objects.

Use "builder" for objects whose purpose is helping with the creation of an immutable object. Name builder methods the same as the field they're setting, without any prefix.


Use a plural name for collections and maps rather than the words "list", "set", "array", etc., unless it's a collection of collections or there are several collections of different types containing the same objects (entities, entityLists).

When it's enough, name maps based on the value type. Otherwise, name it in the "valuesByKeys" format.


Coordinates can be named x, y, and z when it's clear what they represent. If clarification is needed, add a word in front of the coordinate (velocityX, not xVelocity).

Name screen coordinates x and y, rather than left and top.


Write sentences for class, method and field javadocs, starting with an uppercase and ending with a period. Start method docs with verbs, like Gets or Called. Use HTML tags such as <p> if the docs have several paragraphs, as line wraps are converted to spaces in the generated documentation. Feel free to start a new line whenever you feel the current line is too long.

Parameter and @return documentation should use quick descriptions without initial capitalization or punctuation, such as {@code true} if the block placement was successful, {@code false} otherwise. {@return} used in the first sentence can duplicate enclosed text to the return description.

Use {@index} to allow enclosed text to be indexed by the Javadoc search.

Avoid using the @param tag for documentation of methods. Add parameter documentations to the parameter itself instead of adding @param tags to its owner method, so Matcher can update them properly across Minecraft updates. However, you can use the tag for type parameters (such as <T> in public class Lazy<T>), which cannot be documented separately.

Javadoc will take the first sentence, ended by the first ., as a brief description of the member you are documenting. Note that . from abbreviations, such as i.e., count.


Since enigma format does not support file creation, yarn keeps these files in src/packageDocs/java to supply javadocs for packages. Their only purpose is to host Javadoc for yarn packages, which are currently not exported to mappings, and their Javadocs should follow the conventions just like enigma-based Javadocs.


Fabric-hosted Javadocs are generated using JDK 16 Standard Doclet and can use any feature it supports. For example, it has a list of supported tags. You can personally build the documentation with a newer Java version. See the 'Checking Javadoc' section for how to build the documentation locally.

Custom tags

A few additional block tags are supported:

  • @apiNote: API Notes. A few comments for users of the documented API.
  • @implSpec: Implementation Specification. Tells how this method is implemented; usually avoided as yarn doesn't define implementations.
  • @implNote: Implementation Notes. A few comments on the implementation.

Feel free to use these tags and write under these sections.

Linking to other members

Use @link, @linkplain and @see tags to refer to other parts of the code.

You can use the simple name of a class when its import is assumed to exist.

A class is assumed to be imported in the following scenarios:

  • If it is from the java.lang package
  • If it is from the same package as the currently documented class
  • If it is used as part of its API, such as in the signature of the class or its members (methods and fields). See Javadoc's definition of "use" in its -use command line option specification.

If it does not fulfill one of these scenarios, use the full binary name, such as rather than simply Lists. Unlike class naming in enigma, do not use / to separate packages; use . instead.

Use Yarn mappings when referencing Minecraft members, such as rather than net.minecraft.class_3898. The Javadoc task will warn if some links no longer work after a rename.

An example

Assume this is the decompiled content in Enigma, which does not show imports:

 * Assume this class is from the {@code net.example.stuff} package.
 * <p>You can link to {@link Optional} as it's part of the class signature (type parameter bound).
 * <p>You must fully qualify {@link net.example.stuff.basic.BasicStuffUser} when linking as it is not in
 * any signature and is from a different package.
public class Stuff<T extends Optional<?>> {
	 * You can link to {@link Listener} with the simple name as it's part of a field's signature.
	protected Listener listener;

	 * You can link to {@link List} with the simple name as it's part of a method's signature.
	 * <p>You must fully qualify {@link net.example.util.UtilityClass} when linking because it is not part
	 * of any signature (even though it is used in code) and is from a different package.
	public Stuff(List<Integer> opt) {

Checking Javadoc

After writing a Javadoc, you should check its validity. This can easily be done from GitHub using the 'Checks' section, or by clicking the check icon after each commit. For any JDK version, the section titled Run ./gradlew build javadocJar checkMappings mapNamedJar --stacktrace will contain output related to Javadoc generation in the Task :javadoc section.

You can also check Javadoc validity locally using the ./gradlew javadoc (Linux, macOS) or gradlew javadoc (Windows) commands; this will take a while given the sheer size of the Minecraft codebase. After that, you can enter the build/docs/javadoc directory to obtain the generated Javadoc and ensure it renders correctly.

If you are unsure if your Javadoc is correct stylistically, we recommend you to run the javadoc task and check its output, as described in the previous paragraph.

Game content capitalization

When describing content in the game itself, do not use capitalization. For example, the following is incorrect:

The quick Snow Fox jumped over the tamed Wolf.

The following is acceptable:

The quick snow fox jumped over the tamed wolf.

In order to hint that the description references the game's content, inline links may be used.

Mojang names

Do not use names from Mojang's obfuscation maps.

Use names that match names in strings in the vanilla code, unless that string is outdated or inaccurate. This avoids confusion, especially from new modders who may not understand what a class exception message is referring to.

Even if a known Mojang name doesn't appear in any strings, it's a good idea to use it since the official name is a good indicator of the class's actual purpose and makes it less likely the name will have to be changed in the future. For example, don't name a class that Mojang calls BedrockBlock NoSpawningBlock, even if its only purpose is to disable mob spawning, because Mojang may decide to override more methods in that class, breaking mods that were using it in an unexpected way.

There are however three exceptions to this rule:

Things to avoid

Don't name methods based on implementation details. Names should describe what methods do, not how they work.

Avoid including Java-related information in names. For example, don't prefix class names with I, or Enum and don't prefix methods with private. Instead, try to find meaningful names to describe differences between classes. In the case of abstract classes, this may involve renaming subclasses to more specific names.