index.md

title	Class Tweakers
description	Learn what class tweakers are, and how to set them up.
authors	cassiancc Earthcomputer its-miroma MildestToucan

Class tweakers, known as access wideners prior to gaining further functionality, are used to complement Mixin's bytecode manipulation by providing additional transformation tools and allowing for certain runtime modifications to be visible from the development environment.

Class tweakers are not specific to a given Minecraft version, but are only available starting from Fabric Loader 0.18.0, and may only target Vanilla Minecraft classes.

Setup {#setup}

File Format {#file-format}

Class tweaker files are conventionally named after your modid, appended with .classtweaker to help IDE plugins recognize them. They should be stored in resources.

The file must have the following header as its first line:

classTweaker v1 named

Class tweaker files can have blank lines and comments starting with #. Comments can start at the end of a line.

Whilst the specific syntax depends on the feature, modifications are each declared on separate lines. An entry's elements can be separated using any whitespace, including tabs.

Specifying The File Location {#specifying-the-file-location}

The class tweaker file's location must be specified in your build.gradle and fabric.mod.json files. Remember that you must also depend on Fabric Loader 0.18.0 or above to use class tweakers.

The specifications are still named after access wideners for backward compatibility reasons.

build.gradle {#build-gradle}

@code lang=gradle:no-line-numbers transcludeWith=:::classtweaker-setup:gradle:::

fabric.mod.json {#fabric-mod-json}

...

"accessWidener": "example-mod.classtweaker",

...

After specifying the file location in your build.gradle file, make sure to reload your Gradle project in the IDE.

Validating the File {#validating-the-file}

By default, class tweaker will ignore entries referencing modification targets that cannot be found. To check if all the classes, fields and methods specified in the file are valid, run the validateAccessWidener Gradle task.

Errors will point out any invalid entry, but they can be about which part of an entry is invalid.