CLI Frameworks for Kotlin: Clikt, kotlinx-cli, picocli |…

CLI frameworks for Kotlin: building powerful console applications

Kotlin is a modern language that is great not only for Android or server-side development, but also for creating console (CLI) applications. To avoid writing argument parsing manually, there are specialized frameworks. In this article, we will cover three of the most popular solutions: Clikt, kotlinx-cli, and picocli. You will learn their features, see code examples, and be able to choose the right tool for your project.

Why do you need a CLI framework?

Creating command-line utilities is a task that quickly becomes complex: you need to handle flags, options, positional arguments, and output help text. Manual implementation leads to errors and code duplication. Frameworks offer ready-made mechanisms:

Declarative description of the command interface
Automatic help generation (--help)
Input validation
Support for subcommands (git style)
Type safety

1. Clikt — the most "Kotlin-like" framework

Clikt (https://github.com/ajalt/clikt) is a pure Kotlin library that uses DSL and delegated properties. It does not depend on Java annotations and offers an intuitive API.

Installation

// build.gradle.ktsimplementation("com.github.ajalt.clikt:clikt:4.2.2")

Example: a simple calculator

import com.github.ajalt.clikt.core.CliktCommandimport com.github.ajalt.clikt.parameters.arguments.argumentimport com.github.ajalt.clikt.parameters.options.optionimport com.github.ajalt.clikt.parameters.types.int

class Calc : CliktCommand() {    val a: Int by argument()    val b: Int by argument()    val multiply by option("--mult", "-m", help = "Multiply instead of adding").flag()

    override fun run() {        val result = if (multiply) a * b else a + b        echo("Result: $result")    }}

fun main(args: Array<String>) = Calc().main(args)

Run: kotlin calc 5 3 --mult → Result: 15.

Advantages of Clikt:

Full integration with Kotlin (DSL, delegates)
Powerful validation system (custom validators)
Support for subcommands of any depth
Automatic man page generation
Active community and updates

2. kotlinx-cli — a lightweight solution from JetBrains

kotlinx-cli is an experimental library that is part of the Kotlin ecosystem. It is minimalistic and suitable for small utilities.

Installation

// build.gradle.ktsimplementation("org.jetbrains.kotlinx:kotlinx-cli:0.3.6")

Example: a greeting

import kotlinx.cli.*

fun main(args: Array<String>) {    val parser = ArgParser("greet")    val name by parser.option(ArgType.String, shortName = "n", description = "Name")        .default("world")    val times by parser.option(ArgType.Int, shortName = "t", description = "Number of times")        .default(1)

    parser.parse(args)

    repeat(times) {        println("Hello, $name!")    }}

Run: kotlin greet -n Kotlin -t 2 → Hello, Kotlin! (twice).

Features of kotlinx-cli: