Top 10 Kotlin Frameworks for Web Development: From A to Z

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Introduction: Why Kotlin is the Ideal Choice for Web Development?

Kotlin is rapidly conquering the world of backend development. This language, created by JetBrains, combines conciseness, safety, and full compatibility with Java. Thanks to this, Kotlin has become the second official language for Android (after Java) and is actively used in server applications, microservices, and REST APIs.

However, choosing the right framework can be a real headache. In this article, we have compiled 10 best Kotlin frameworks for web development — from lightweight libraries to full-fledged enterprise-level platforms. We will review each tool with code examples so you can quickly assess its capabilities.

1. Ktor: Lightweight and Asynchronous

Ktor is the official framework from JetBrains, created specifically for Kotlin. It is fully asynchronous, built on coroutines, and is ideal for microservices and REST APIs.

Example of a simple server on Ktor

import io.ktor.server.engine.*import io.ktor.server.netty.*import io.ktor.routing.*import io.ktor.http.*import io.ktor.application.*import io.ktor.response.*

fun main() {    embeddedServer(Netty, port = 8080) {        routing {            get("/") {                call.respondText("Hello, Kotlin!", ContentType.Text.Plain)            }        }    }.start(wait = true)}

Pros: minimalistic code, built-in WebSocket support, flexible configuration. Cons: fewer built-in features compared to Spring.

2. Spring Boot: The Power of the Enterprise World

Spring Boot remains the most popular framework in the Java ecosystem. Thanks to official Kotlin support, you can use all the advantages of Spring (DI, JPA, Security) with Kotlin syntax.

Example of a controller on Spring Boot + Kotlin

import org.springframework.web.bind.annotation.*

@RestController@RequestMapping("/api")class HelloController {

    @GetMapping("/hello")    fun hello(@RequestParam name: String) = "Hello, $name!"}

Pros: huge community, thousands of ready-made starters, excellent documentation. Cons: heavy startup, a lot of "magic" in configuration.

3. Javalin: Simplicity and Performance

Javalin is a lightweight framework inspired by Express.js and Spark. It does not use reflection, which makes it very fast.

Example API on Javalin

import io.javalin.Javalin

fun main() {    val app = Javalin.create().start(7000)    app.get("/") { ctx -> ctx.result("Hello from Javalin!") }}

Pros: intuitive API, excellent documentation, WebSocket support. Cons: fewer features for complex applications.

4. http4k: Functional Approach

http4k is a framework that treats an HTTP application as a pure function. It is ideal for testing and functional programming.

Example handler on http4k

import org.http4k.core.*import org.http4k.server.*import org.http4k.routing.*

fun main() {    val app: HttpHandler = routes(        "/hello" bind GET to { request: Request ->            Response(Status.OK).body("Hello, ${request.query("name") ?: "World"}!")        }    )    app.asServer(Jetty(8080)).start()}

Pros: modularity, excellent testability, Serverless support. Cons: steep learning curve for beginners.