Kotlin

Kotlin is a statically typed, multiplatform programming language developed by JetBrains. This repository contains the Kotlin compiler (the K1 and K2/FIR frontends, plus JVM, JS, WebAssembly, and Native backends), the standard library and reflection libraries, the Analysis API for IDE tooling, build-system integrations (Gradle, Maven, JPS), the script engine, and a collection of compiler plugins (Compose, kotlinx.serialization, kapt, parcelize, allopen, lombok, atomicfu, and others).

The codebase is large (over 4 million lines of Kotlin and Java), has been under continuous development since 2010, and spans a frontend that produces FIR (Frontend Intermediate Representation) and IR (backend Intermediate Representation), four target backends, and a substantial ecosystem of tooling. It is organized as a Gradle monorepo. The Kotlin/Native backend pulls in LLVM and a separate set of C/C++ runtime sources.

What is in this wiki

This wiki is generated from the source code on the default master branch. It is intentionally written as a map for engineers landing in the repository: where the major subsystems live, how they fit together, and how to do common tasks like building, testing, and contributing.

Recommended starting points:

• Architecture — top-level structure, the K1/K2 frontend split, the IR layer, and the backends
• Getting started — build, run, and test the compiler and libraries
• Glossary — Kotlin-specific vocabulary (FIR, IR, klib, KGP, KMP, etc.)
• How to contribute — workflow, testing, conventions
• Compiler — the heart of the repository
• Standard library and tools — stdlib, reflect, scripting, build-system plugins
• Compiler plugins — Compose, serialization, kapt, parcelize, atomicfu, etc.

What is not here

The IntelliJ IDEA Kotlin plugin lives in a separate repository, JetBrains/intellij-community. The Analysis API in this repo is what powers it, but the IDE-side code is not in this tree.

Several Kotlin-related projects live in their own repositories: kotlinx.coroutines, kotlinx.serialization runtime, kotlinx.datetime, Compose Multiplatform, etc. This repository builds the compiler plugin for serialization and Compose, but not the runtime libraries.

How releases work

Public Kotlin releases are cut from this repository, with -dev snapshots published to a JetBrains-hosted Maven repository (https://redirector.kotlinlang.org/maven/bootstrap) and stable releases published to Maven Central under org.jetbrains.kotlin. The prepare/ directory contains the assembly logic for the various distributable artifacts (kotlinc, kotlin-compiler-embeddable, kotlin-stdlib, etc.).

Project links

• Site: https://kotlinlang.org/
• Issue tracker: https://youtrack.jetbrains.com/issues/KT (issues are referenced in commits as KT-XXXXX)
• Slack: https://slack.kotlinlang.org/
• Forum: https://discuss.kotlinlang.org/
• TeamCity CI: https://teamcity.jetbrains.com/project.html?projectId=Kotlin