Documentation in Kotlin: Writing Code That Speaks for Itself

Documentation in Kotlin Projects: The Art of Being Understood

Imagine: you open someone else's Kotlin project. The code is beautiful, concise, but... you don't understand what this function is for or what it returns. Sound familiar? Now imagine that this project is your own, but six months later. Documentation in Kotlin is not just politeness to colleagues. It's an investment in the future of your code.

In this article, we'll break down the best practices for documenting Kotlin projects. You'll learn how to use KDoc, Dokka, and plain comments so that your code speaks for itself. Let's go!

Why Documentation in Kotlin Isn't Boring

Kotlin is a language created for people. It reads like English, and its syntax eliminates boilerplate code. But even the most elegant code can be a mystery without documentation. Especially when it comes to:

\n
• Complex business logic;
\n
• Libraries and APIs used by other developers;
\n
• Android projects with a long lifecycle;
\n
• Enterprise solutions where staff turnover is the norm.
\n

Good Kotlin documentation solves three tasks: explains "what" the code does, "why" it does it, and "how" to use it. Without it, you risk ending up with code that no one wants to touch (not even yourself).

KDoc: The Main Tool for Documenting Kotlin

KDoc is the JavaDoc equivalent for Kotlin. It uses /** ... */ comments and supports Markdown. It's the de facto standard for documentation in Kotlin projects.

Here's what a basic example looks like:

/**\n * Calculates a discount for a user based on their status.\n *\n * @param price The original price of the item.\n * @param userLevel The user's level (BRONZE, SILVER, GOLD).\n * @return The final price after discount.\n * @throws IllegalArgumentException If price is negative.\n */\nfun calculateDiscount(price: Double, userLevel: UserLevel): Double {\n    // logic\n}

Note: KDoc uses @param, @return, @throws tags. But unlike JavaDoc, you can write Markdown directly inside the comment. This is convenient for lists, links, and formatting.

KDoc Best Practices

\n
• Write for people, not for machines. Don't duplicate what's obvious from the code. Instead of // sets the value, write // Sets the value to be used when calculating taxes.
\n
• Document the public API. Internal functions (private or internal) can be documented briefly or not at all.
\n
• Use @see and @sample. Reference related functions or usage examples.
\n
• Don't forget @receiver for extension functions.
\n

Dokka: Turning Comments into Beautiful Documentation

Dokka is a documentation generator for Kotlin. It can create HTML, Markdown, JavaDoc, and even documentation for multiplatform projects. If you're writing a library or working in a team, Dokka is your best friend.

Installation is simple. Add the plugin to build.gradle.kts:

plugins {\n    id("org.jetbrains.dokka") version "1.9.20"\n}

Then run the command:

./gradlew dokkaHtml

Dokka will generate a build/dokka/html folder with beautiful documentation, including all your KDoc comments, class hierarchy, and even links to source files.

Dokka Tips

\n
• Configure the project logo and description in dokkaConfiguration;
\n
• Use @suppress to hide undesired