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.
1,000+ codders enrolled
213 lessons212 challenges826 quiz questions
- Beginner friendly
AI-assisted coding help
Hands-on interactive lessons
Audio narration on every lesson
Quizzes to test your knowledge
Free certificate of completion
Syllabus
Section 1
Fundamentals
Start sectionStartBuild a strong foundation with essential concepts and basic skillsIntroduction
4 lessons415Variables
7 lessons1330Nullability
7 lessons1130Operators Part 1
5 lessons920Operators Part 2
5 lessons920Decision Making
6 lessons1125Basic IO
6 lessons1020Bill Split Calculator
Project5 lessons5Loops
9 lessons1635Functions
8 lessons1430FizzBuzz with a Twist
Project4 lessons4Lists Basics
7 lessons1225Iterating Over Sequences
5 lessons920Lists Advanced
5 lessons920Daily Expense Tracker
Project7 lessons7Final Challenges
3 lessons3Section 2
Logic & Flow
Start sectionStartBuild on Kotlin Fundamentals with maps, sets, nested collections, lambdas, data pipelines, text processing and error handling. Apply your skills in Contact Book and Inventory projects, mastery challenges and final challenges.Maps Part 1
5 lessons920Maps Part 2
5 lessons920Sets and Membership
5 lessons920Nested Collections
5 lessons920Project - Contact Book
5 lessons5Function Values
5 lessons920Collection Pipelines
5 lessons920Sorting and Grouping
5 lessons920Advanced Control Flow
5 lessons920Text Processing
5 lessons920Error Handling
5 lessons920Project - Inventory
5 lessons5Final Challenges
3 lessons3Section 3
Object Oriented Programming
Start sectionStartModel programs with classes and objects. Learn constructors, properties, visibility, objects and companions, inheritance, interfaces, polymorphism, data, enum and sealed classes, generics and classic design patterns, then build a Library Management project.Classes and Objects
6 lessons1140Properties and Encapsulation
5 lessons932Objects and Companions
5 lessons932Inheritance
5 lessons932Interfaces
5 lessons932Polymorphism
5 lessons932Special Classes
5 lessons932Generics
5 lessons932Design Patterns Part 1
4 lessons832Design Patterns Part 2
4 lessons832Project: Library Management
5 lessons58Final Challenges
3 lessons3
Learn by Doing
Write real code, query databases, build websites, and master AI prompts. Our interactive lessons cover every skill modern developers need.
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January 2026
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Double or Nothing
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Code Anywhere
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.
You're Not Alone
Compete on global leaderboards, invite friends to earn rewards, and celebrate each other's wins. Coding is better with friends!
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Promotion zoneEvery 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.
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.
Earn a Certificate
Earn certificates for every course you complete. Add them to your LinkedIn profile and resume to showcase your coding expertise to employers.
Certificate of CompletionPython Fundamentals
Add to LinkedInWhy 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:
valvsvarand type inference, null safety with?.,?:and!!, string templates,ifandwhenas expressions, ranges and loops, functions with default and named arguments, andListvsMutableListwith 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
whenoverif, whyvaldoesn'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.
Do I get a certificate after the Kotlin course?
Yes. Finishing the Kotlin course earns you a free certificate of completion with a verification link you can share on LinkedIn or add to your CV, next to any Android or Kotlin projects you build afterwards.
