ModernCalcs

Kotlin Formatter

Indent
data class User(val name: String, val age: Int, val email: String)

interface Repository<T> {
    fun findById(id: Int): T?
    fun findAll(): List<T>
    fun save(entity: T): T
}

class UserRepository : Repository<User> {
    private val users = mutableListOf<User>()
    override fun findById(id: Int) = users.getOrNull(id)
    override fun findAll() = users.toList()
    override fun save(entity: User): User {
        users.add(entity)
        return entity
    }
    fun findByAge(minAge: Int) = users.filter { it.age >= minAge }
}

fun main() {
    val repo = UserRepository()
    repo.save(User("Alice", 30, "alice@example.com"))
    repo.save(User("Bob", 25, "bob@example.com"))
    val adults = repo.findByAge(28)
    adults.forEach { println("${it.name}: ${it.email}") }
}

Kotlin style guide recommends 4-space indentation. For IntelliJ-standard formatting, use Code → Reformat Code (⌘⌥L / Ctrl+Alt+L) in the IDE.

Kotlin Formatter: Indent and Beautify Kotlin Code

Kotlin is used for Android development, backend services (Ktor, Spring), and multiplatform apps. This formatter applies consistent brace-depth indentation to Kotlin code — useful for reviewing AI-generated code, formatting snippets from documentation, or cleaning up pasted code before opening it in IntelliJ or Android Studio.

Formula
// Input: flat class UserService { private val users = mutableListOf<User>() fun add(user: User) { users.add(user) } fun findByAge(min: Int) = users.filter { it.age >= min } } // Output: indented class UserService { private val users = mutableListOf<User>() fun add(user: User) { users.add(user) } fun findByAge(min: Int) = users.filter { it.age >= min } }

Kotlin style guide recommends 4-space indentation. Single-expression functions on one line are preserved as-is.

Kotlin vs Java Formatting

Kotlin uses the same { } block delimiters as Java but adds trailing lambda syntax, single-expression functions, and when expressions. This formatter handles all { } blocks identically — trailing lambdas on a single line have balanced braces and do not affect indentation.

Data Classes and Interfaces

Kotlin data classes (data class User(val name: String, val age: Int)) are typically one-liners and are formatted without added newlines. Regular class bodies with members use { } blocks and are indented correctly. Interface declarations work the same way.

IntelliJ Code Style

IntelliJ IDEA and Android Studio have a powerful built-in Kotlin formatter accessible via Code → Reformat Code (⌘⌥L / Ctrl+Alt+L). It enforces line length, blank lines between declarations, and more. This browser tool handles indentation only — use the IDE formatter for committed code.

Practical Examples

Formatting Kotlin from Documentation

Kotlin documentation and blog posts often show unindented code snippets.

  • 1.Paste the Kotlin snippet
  • 2.Formatter applies 4-space indentation (Kotlin style guide standard)
  • 3.Review class and function structure
  • 4.Copy to your editor or IDE for further editing

What Gets Formatted

  • class, object, interface, fun, if, when, for, while blocks
  • Trailing lambdas { } on same line treated as inline
  • 4-space indentation default (Kotlin style guide)
  • Multiple blank lines collapsed

Good Use Cases

  • Formatting AI-generated Kotlin code
  • Reviewing Kotlin snippets from documentation or Stack Overflow
  • Cleaning up pasted code before opening in Android Studio
  • Teaching Kotlin code structure to Java developers

Frequently Asked Questions

What indentation does the Kotlin style guide recommend?

The Kotlin style guide (and Android style guide) recommend 4-space indentation for all blocks. 2-space indentation is sometimes seen in projects with deeply nested code, but 4 spaces is the official recommendation.

Does this handle Kotlin lambda syntax?

Lambda expressions use { } blocks and are indented like any other block. Single-expression functions (val double = { x: Int -> x * 2 }) stay on one line since they have matching braces on the same line.

What about trailing lambdas?

Trailing lambda syntax like list.filter { it.age > 18 } has the { } on the same line, so the formatter treats it as a balanced inline block and does not change the indentation.

How do I format Kotlin in IntelliJ or Android Studio?

Use Code → Reformat Code (⌘⌥L on Mac, Ctrl+Alt+L on Windows/Linux). You can also configure the formatter in Settings → Editor → Code Style → Kotlin to match your team's style guide.

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