Ktor

You decided to build a backend with Kotlin. Good choice. But now you face another decision: Ktor or Spring Boot? Both are great frameworks. Both support Kotlin. But they are very different in philosophy, design, and use cases. Let’s compare them honestly. The Big Picture Ktor is a lightweight, modular framework built by JetBrains. It is Kotlin-native, coroutine-based, and you add features as plugins. Spring Boot is a full-featured, batteries-included framework from VMware (now Broadcom). It started as a Java framework and added Kotlin support later. ...

You know Kotlin. You build Android apps, maybe KMP apps. But what about the backend? Every app needs a server. An API to fetch data from. A backend to store users, handle payments, send notifications. You could learn Node.js and Express. Or Python and FastAPI. Or Java and Spring Boot. Or you could use the Kotlin you already know — and build your backend with Ktor. What is Ktor? Ktor is a backend framework built by JetBrains — the same company that created Kotlin. It lets you build web servers, REST APIs, microservices, and web applications using Kotlin. ...

In the previous tutorial, we set up the Notes app architecture with a local database and shared ViewModels. Everything works offline. But real apps need to sync with a server. In this tutorial, we build the shared data layer — adding a Ktor API client, Data Transfer Objects (DTOs), an offline-first sync pattern, and a database migration. All of this code lives in commonMain and runs on both Android and iOS. ...

Every app needs to talk to the internet. On Android, you use Retrofit. On iOS, you use URLSession. Two different libraries, two different APIs, two different codebases. In KMP, you use Ktor Client — one networking library that works on every platform. Write your API calls once in commonMain, and they work on Android, iOS, Desktop, and Web. What is Ktor? Ktor is a networking framework by JetBrains (the same team behind Kotlin). The client side lets you make HTTP requests from shared code. ...

In the previous tutorial, you built a CLI tool. Now let’s build a REST API. Ktor is Kotlin’s official framework for building asynchronous servers and clients. It is lightweight, flexible, and uses Kotlin coroutines. In this tutorial, you will learn: Setting up Ktor Routing (GET, POST, PUT, DELETE) JSON serialization with Content Negotiation In-memory storage Path parameters and query parameters Error handling with StatusPages Testing with ktor-server-test-host What We’re Building A Notes API with CRUD operations: ...