Fabric Loom, or just Loom for short, is a Gradle plugin for development of mods in the Fabric ecosystem. Loom provides utilities to install Minecraft and mods in a development environment so that you can link against them with respect to Minecraft obfuscation and its differences between distributions and versions. It also provides run configurations for use with Fabric Loader, Mixin compile processing and utilities for Fabric Loader's jar-in-jar system.

• minecraft: Defines the version of Minecraft to be used in the development environment.
• mappings: Defines the mappings to be used in the development environment.
• modCompile, modImplementation, modApi and modRuntime: Augmented variants of compile, implementation, api and runtime for dependencies that should be remapped to match the mappings in the development environment, generally for depending on mods.
• include: Declares a dependency that should be included as a jar-in-jar in the remapJar output. This dependency configuration is not transitive.

• cleanLoomBinaries: For the configured version of Minecraft and the configured mappings, deletes the merged Minecraft jar, the intermediary Minecraft jar and the mapped Minecraft jar from the user cache.
• cleanLoomMappings: For the configured version of Minecraft and the configured mappings, deletes the mappings, the intermediary Minecraft jar and the mapped Minecraft jar from the user cache. Also clears the root project build cache.
• migrateMappings: Migrates the current source to the specified mappings. See migratemappings.
• remapJar: Produces a jar containing the remapped output of the jar task. Also appends any included mods for jar-in-jar.
• genSources: Delegates to two tasks. genSourcesDecompile decompiles the mapped Minecraft jar using FernFlower to create a sources jar and additionally generates a linemap. genSourcesRemapLineNumbers then applies the generated linemap to produce a linemapped jar which re-aligns line numbers in the binary and source jars. The linemapped jar replaces the mapped jar.
• downloadAssets: Downloads the asset index and asset objects for the configured version of Minecraft into the user cache.
• genIdeaWorkspace: Depends on idea and genSources. Installs run configurations in the ItelliJ project of the root project and creates the run directory if it does not already exist.
• genEclipseRuns: Depends on genSources. Installs Eclipse run configurations and creates the run directory if it does not already exist.
• vscode: Depends on genSources. Generates or overwrites a Visual Studio Code launch.json file with launch configurations in the .vscode directory and creates the run directory if it does not already exist.
• remapSourcesJar: Only exists if an AbstractArchiveTask sourcesJar exists. Produces a jar containing the remapped output of the sourcesJar.
• runClient: A JavaExec task to launch Fabric Loader as a Minecraft client.
• runServer: A JavaExec task to launch Fabric Loader as a Minecraft dedicated server.

• Applies the following plugins: java, eclipse and idea.
• Adds the following Maven repositories: Fabric https://maven.fabricmc.net/, Mojang https://libraries.minecraft.net/, Maven Central and JCenter.
• Configures idea extension to exclude directories .gradle, build, .idea and out, to download javadocs sources and to inherit output directories.
• Configures the idea and eclipse tasks to be finalized by genIdeaWorkspace and genEclipseRuns respectively.
• Adds net.fabricmc:fabric-mixin-compile-extensions and its dependencies with the annotationProcessor dependency configuration.
• Adds the output of remapJar as an archives artifact and remapJar is made a dependency of build.
• If an AbstractArchiveTask sourcesJar exists, adds the output of remapSourcesJar task as an archives artifact and remapSourcesJar is made a dependency of build.

Run configurations are generated from the fabric-installer.json file of Fabric Loader if it installed as a dependency.

• net.fabricmc.loom.task.RemapJarTask
• net.fabricmc.loom.task.RemapSourcesJarTask

Loom does quite a few things behind the scenes to create a development environment with Minecraft.

1. Downloads the client and server jar from official channels for the configured version of Minecraft.
2. Merges the client and server jar to produce a merged jar with @Environment and @EnvironmentInterface annotations.
3. Downloads the configured mappings.
4. Remaps the merged jar with intermediary mappings to produce an intermediary jar.
5. Remaps the intermediary jar with yarn mappings to produce a mapped jar.
6. Optional: Decompiles the mapped jar to produce a mapped sources jar and linemap, and applies the linemap to the mapped jar.
7. Adds dependencies of Minecraft.
8. Downloads Minecraft assets.
9. Remaps mod-augmented dependencies.

• ${GRADLE_HOME}/caches/fabric-loom: The user cache, a cache shared by all Loom projects for a user. Used to cache Minecraft assets, jars, merged jars, intermediary jars and mapped jars.
• .gradle/loom-cache: The root project persistent cache, a cache shared by a project and its subprojects. Used to cache remapped mods as well as generated included mod jars.
• build/loom-cache: The root project build cache.
• **/build/loom-cache: The (sub)project build cache.