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Learn Kotlin

A free, interactive online Kotlin course for beginners. You write and run real Kotlin in every lesson, get AI hints the moment you're stuck, and earn a free certificate when you finish - no Android Studio, no JDK, nothing to install.

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View syllabusKotlin playground

1,000+ codders enrolled

93 lessons79 challenges290 quiz questions

  • Beginner friendly
  • sparkles iconAI-assisted coding help
  • hint iconHands-on interactive lessons
  • volume On iconAudio narration on every lesson
  • quiz iconQuizzes to test your knowledge
  • certificate iconFree certificate of completion

Syllabus

1 sections3 projects93 lessons79 challenges290 quiz questions
  1. Section 1

    Fundamentals

    Start sectionStartExpandCollapse    Build a strong foundation with essential concepts and basic skills93 lessons133 challenges290 questions3 projects

    Introduction

    4 lessons415

    Variables

    7 lessons1330

    Nullability

    7 lessons1130

    Operators Part 1

    5 lessons920

    Operators Part 2

    5 lessons920

    Decision Making

    6 lessons1125

    Basic IO

    6 lessons1020

    Bill Split Calculator

    Project5 lessons1

    Loops

    9 lessons1635

    Functions

    8 lessons1430

    FizzBuzz with a Twist

    Project4 lessons1

    Lists Basics

    7 lessons1225

    Iterating Over Sequences

    5 lessons920

    Lists Advanced

    5 lessons920

    Daily Expense Tracker

    Project7 lessons1

    Final Challenges

    3 lessons3
What you get
Everything you'll use to learn to code

Learn by Doing

Write real code, query databases, build websites, and master AI prompts. Our interactive lessons cover every skill modern developers need.

playground.js
Code Editor
1const greeting = "Hello, Coddy!"
2function sayHi(name) {
3    return greeting + " " + name
4}
5
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Input
"Alex"
Output
"Hello, Coddy! Alex"

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Double or Nothing

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Take your coding journey on the go! No setup, no downloads - just open and start coding. Available on iOS, Android and Web with 4.9 star ratings.

Python
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Variables
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CONTINUE
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Journey
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You're Not Alone in This

Compete on global leaderboards, invite friends to earn rewards, and celebrate each other's wins. Coding is better with friends!

Challenger League
Challenger LeagueTop 7 advance
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Every way to learn

Read, listen, test yourself, ask the AI, or look up anything you've already covered. Every lesson meets you where you are.

Intro to Variables
Audio

A variable is a named container that stores a value you can reference later in your program.

In Python, you create one by writing the name, an equals sign, then the value you want to store.

The value can change over time - reassigning the name simply points it to a new value.

1xSarah

Prove Your Skills

Earn certificates for every course you complete. Add them to your LinkedIn profile and resume to showcase your coding expertise to employers.

CoddyCertificate of Completion
This certifies thatJohn Doehas successfully completed
python iconPython Fundamentals
Verified
DateJan 2026
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Why learn Kotlin with Coddy

  • Write and run real Kotlin in your browser. No Android Studio, no IntelliJ, no JDK to set up - every lesson compiles your code with the Kotlin compiler server-side and shows the output and any compiler errors instantly, on desktop or phone.
  • The Kotlin that Android and backend developers actually write: val vs var and type inference, null safety with ?., ?: and !!, string templates, if and when as expressions, ranges and loops, functions with default and named arguments, and List vs MutableList with the collection methods you use every day.
  • AI hints explain the parts of Kotlin that trip up beginners - why the compiler refuses a nullable, when to use when over if, why val doesn't mean the list is immutable - so you build the right mental model from the first lesson, without waiting for a forum reply.
  • Build real programs, not just exercises: a bill-split calculator that reads input and formats output, FizzBuzz with a twist, and a daily expense tracker with error handling, totals, and averages. Each one is written step by step across a chapter.

Frequently asked questions about learning Kotlin

What is Kotlin used for?

Kotlin is a modern, statically typed language that runs on the JVM and compiles to JavaScript and native code. Its biggest use is Android - Google made it the preferred language for Android development in 2019, and most new Android apps are written in it. It's also widely used for backend services with Spring Boot and Ktor, for cross-platform apps with Kotlin Multiplatform and Compose Multiplatform, and for build scripts with Gradle.

Is Kotlin hard to learn?

No - Kotlin is one of the friendlier languages to start with. The syntax is concise, type inference means you rarely spell out types, and the compiler catches null errors before your program runs. If you already know Java, JavaScript, or Python, most of it will feel familiar. This course starts from Hello World and introduces one idea per lesson, so you never need prior programming experience.

Should I learn Kotlin or Java first?

If your goal is Android, start with Kotlin - it's what Google recommends, what the official Android docs use, and what Jetpack Compose is built for. Kotlin is fully interoperable with Java, so you can read and call Java code from day one and pick up Java later if a job requires it. If your goal is enterprise backend work or university coursework that is taught in Java, Java first is still a reasonable choice.

How long does it take to learn Kotlin?

The basics - variables, null safety, conditionals, loops, functions, and lists - take two to four weeks of daily practice, which is what this course covers. Being comfortable enough to build a small Android app or a Ktor backend usually takes another two to three months, mostly spent learning the framework rather than the language itself.

Do I need Android Studio to learn Kotlin?

Not to learn the language. Kotlin is a general-purpose language and every lesson here runs in your browser, so you can focus on the language itself before touching an IDE. Once you move on to Android, you'll install Android Studio - and everything you learned here carries over unchanged.

Can I learn Kotlin online for free?

Yes. The interactive Kotlin course is free - all the lessons, coding exercises, the projects, and the certificate. Kotlin compiles and runs server-side, so you don't need to install the JDK, IntelliJ, or Android Studio to start writing real code.
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Learn Kotlin with Coddy

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