Kotlin is a modern, expressive, and statically typed programming language developed by JetBrains. Designed for building robust, maintainable, and performant applications, Kotlin supports multiple platforms including JVM, Android, JavaScript, WebAssembly, and Native (via LLVM), enabling true code sharing across mobile, web, desktop, and server.

• About
• Why Kotlin?
• Kotlin Multiplatform capabilities
• Editing Kotlin
• Build environment requirements
• Building
• Important Gradle tasks
• Working with the project in IntelliJ IDEA
• Dependency verification
• Using -dev versions
• Community and Support
• License
• Contributing
• Kotlin Foundation

Welcome to Kotlin!
Kotlin is a concise multiplatform language developed by JetBrains and contributors.

Some handy links:

• Kotlin Site
• Getting Started Guide
• Try Kotlin
• Kotlin Standard Library
• Issue Tracker
• Kotlin YouTube Channel
• Forum
• Kotlin Blog
• Subscribe to Kotlin YouTube channel
• Follow Kotlin on Twitter
• Public Slack channel
• TeamCity CI build
• Kotlin Foundation

Kotlin stands out as a modern programming language that combines clarity, expressiveness, and robust engineering practices. Its design philosophy is focused on developer productivity, safety, and seamless integration with existing ecosystems.

• Full Java Interoperability
  Kotlin is 100% interoperable with Java, allowing teams to adopt it gradually in existing codebases. Developers can use all existing Java libraries, frameworks, and tools without any modification.

• Multiplatform Development
  Kotlin supports true multiplatform development, enabling code sharing across Android, iOS, JVM, JavaScript, WebAssembly, and native platforms through Kotlin Multiplatform. This significantly reduces duplication and improves maintainability.

• Concise and Readable Syntax
  Kotlin reduces boilerplate code through smart language design, making codebases more compact, readable, and easier to maintain. Common programming patterns are supported natively in the language, resulting in cleaner code.

• Strong Type System and Null Safety
  Kotlin’s type system helps eliminate entire classes of bugs, especially null pointer exceptions. Null safety is built into the type system, making your applications more stable and secure.

• Tooling and IDE Support
  Developed by JetBrains, Kotlin has first-class support in IntelliJ IDEA and Android Studio. It benefits from deep tooling integration, including code completion, refactoring, debugging, linting, and more.

• Modern Language Features
  Kotlin includes powerful features such as extension functions, coroutines for asynchronous programming, sealed classes, data classes, smart casts, and inline functions—providing developers with expressive and flexible language constructs.

• Open Source and Backed by JetBrains
  Kotlin is an open-source language governed by the Kotlin Foundation. It’s actively developed and maintained by JetBrains with contributions from a vibrant and growing global community.

• Safe and Production-Ready
  Kotlin is battle-tested in production by companies like Google, Pinterest, Netflix, Uber, and Coursera. It is the preferred language for Android app development and is used at scale in backend, web, and cross-platform applications.

• Actively Evolving Ecosystem
  The Kotlin ecosystem is growing rapidly, with tools, libraries, and frameworks emerging to support everything from web development (e.g., Ktor, kotlinx.html) to data science, server-side applications, and native development.

Support for multiplatform programming is one of Kotlin’s key benefits. It reduces time spent writing and maintaining the same code for different platforms while retaining the flexibility and benefits of native programming.

• Kotlin Multiplatform Mobile for sharing code between Android and iOS
• Getting Started with Kotlin Multiplatform Mobile Guide
• Kotlin Multiplatform Benefits
• Share code on all platforms
• Share code on similar platforms

• Kotlin IntelliJ IDEA Plugin (source code)
• Kotlin Eclipse Plugin
• Kotlin Sublime Text Package

This repository is using Gradle toolchains feature to select and auto-provision required JDKs from AdoptOpenJdk project.

Alternatively, it is still possible to only provide required JDKs via environment variables (see gradle.properties for supported variable names). To ensure Gradle uses only JDKs from environmental variables - disable Gradle toolchain auto-detection by passing -Porg.gradle.java.installations.auto-detect=false option (or put it into $GRADLE_USER_HOME/gradle.properties).

On Windows you might need to add long paths setting to the repo:

git config core.longpaths true 

The project is built with Gradle. Run Gradle to build the project and to run the tests using the following command on Unix/macOS:

./gradlew <tasks-and-options>

or the following command on Windows:

gradlew <tasks-and-options>

On the first project configuration gradle will download and setup the dependencies on

• intellij-core is a part of command line compiler and contains only necessary APIs.
• idea-full is a full blown IntelliJ IDEA Community Edition to be used in the plugin module.

These dependencies are quite large, so depending on the quality of your internet connection you might face timeouts getting them. In this case, you can increase timeout by specifying the following command line parameters on the first run:

./gradlew -Dhttp.socketTimeout=60000 -Dhttp.connectionTimeout=60000

• clean - clean build results
• dist - assembles the compiler distribution into dist/kotlinc/ folder
• install - build and install all public artifacts into local maven repository
• coreLibsTest - build and run stdlib, reflect and kotlin-test tests
• gradlePluginTest - build and run gradle plugin tests
• compilerTest - build and run all compiler tests

To reproduce TeamCity build use -Pteamcity=true flag. Local builds don't run proguard and have jar compression disabled by default.

OPTIONAL: Some artifacts, mainly Maven plugin ones, are built separately with Maven. Refer to libraries/ReadMe.md for details.

To build Kotlin/Native, see kotlin-native/README.md.

It is recommended to use the latest released version of Intellij IDEA (Community or Ultimate Edition). You can download IntelliJ IDEA here.

After cloning the project, import the project in IntelliJ by choosing the project directory in the Open project dialog.

For handy work with compiler tests it's recommended to use Kotlin Compiler Test Helper

We have a dependencies verification feature enabled in the repository for all Gradle builds. Gradle will check hashes (md5 and sha256) of used dependencies and will fail builds with Dependency verification failed errors when local artifacts are absent or have different hashes listed in the verification-metadata.xml file.

It's expected that verification-metadata.xml should only be updated with the commits that modify the build. There are some tips how to perform such updates:

• Delete components section of verification-metadata.xml to avoid stockpiling of old unused dependencies. You may use the following command:

#macOS
sed -i '' -e '/<components>/,/<\/components>/d' gradle/verification-metadata.xml
#Linux & Git for Windows
sed -i -e '/<components>/,/<\/components>/d' gradle/verification-metadata.xml

• Re-generate dependencies with Gradle's --write-verification-metadata command (verify update relates to your changes)

./gradlew --write-verification-metadata sha256,md5 -Pkotlin.native.enabled=true resolveDependencies

resolveDependencies task resolves dependencies for all platforms including dependencies downloaded by plugins.

You can also use ./scripts/update-verification-metadata.sh script which includes both of these steps

Keep in mind:

• If you’re adding a dependency with OS mentioned in an artifact name (darwin, mac, osx, linux, windows), remember to add them to implicitDependencies configuration or update resolveDependencies task if needed. resolveDependencies should resolve all dependencies including dependencies for different platforms.
• If you have a local.properties file in your Kotlin project folder, make sure that it doesn't contain kotlin.native.enabled=false. Otherwise, native-only dependencies may not be added to the verification metadata. This is because local.properties has higher precedence than the -Pkotlin.native.enabled=true specified in the Gradle command.

We publish -dev versions frequently.

For -dev versions you can use the list of available versions and include this maven repository:

maven("https://redirector.kotlinlang.org/maven/bootstrap")

Kotlin has a strong, welcoming, and rapidly growing global community. Whether you're a beginner or an experienced developer, there's a wide range of resources available to help you learn, grow, and get involved.

• Kotlin Website – Central hub for all things Kotlin
  https://kotlinlang.org

• Kotlin Documentation – In-depth guides, tutorials, and API reference
  https://kotlinlang.org/docs/home.html

• Kotlin Playground – Write, run, and share Kotlin code directly in the browser
  https://play.kotlinlang.org

• Kotlin Blog – News, release updates, and insights from the Kotlin team
  https://blog.jetbrains.com/kotlin/

• Issue Tracker – Report bugs or request features via JetBrains' YouTrack
  https://youtrack.jetbrains.com/issues/KT

• Kotlin Slack (Public) – Over 30,000 members sharing knowledge and helping each other
  https://slack.kotlinlang.org/

• Kotlin Forums – Ask questions and join discussions with other Kotlin developers
  https://discuss.kotlinlang.org

• Stack Overflow – A large Kotlin tag with thousands of answered questions
  https://stackoverflow.com/questions/tagged/kotlin

• YouTube Channel – Official Kotlin talks, tutorials, and livestreams
  https://www.youtube.com/@kotlin

• Twitter (X) – Follow for news, tips, and community highlights
  https://twitter.com/kotlin

• KotlinConf – The official Kotlin conference hosted by JetBrains
  https://kotlinconf.com

• Community Meetups – Kotlin user groups and community-run events around the world
  https://kotlinlang.org/community/user-groups.html

Kotlin is distributed under the terms of the Apache License (Version 2.0). See license folder for details.

Please be sure to review Kotlin's contributing guidelines to learn how to help the project.

The Kotlin Foundation is a non-profit organization whose mission is to promote and advance the Kotlin ecosystem. You can learn more about the structure and goals of the Kotlin Foundation on its official website.