Top 10 Kotlin Frameworks for Web Development in 2025

Top 10 Kotlin Frameworks for Web Development

Kotlin has firmly established itself as a modern language for backend development. Thanks to full compatibility with Java, concise syntax, and a powerful type system, it has become the #1 choice for many startups and large corporations. In this article, we have compiled the top 10 Kotlin frameworks for web development that will help you build performant and scalable applications.

1. Ktor — Official JetBrains Framework

Ktor is an asynchronous framework from the creators of Kotlin. It is built on coroutines and is ideal for microservices and REST APIs.

Key Features

• Fully asynchronous (Kotlin Coroutines)
• Modular architecture — only connect the plugins you need
• Built-in support for WebSockets, HTTP/2, and SSL
• Simple configuration via DSL

Code Example

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

fun main() {    embeddedServer(Netty, port = 8080) {        routing {            get("/") {                call.respondText("Hello, Kotlin!", ContentType.Text.Plain)            }            get("/api/users/{id}") {                val userId = call.parameters["id"]                call.respond(mapOf("id" to userId, "name" to "User $userId"))            }        }    }.start(wait = true)}

2. Spring Boot — Industry Standard

Spring Boot with Kotlin support is a powerful powerhouse for enterprise development. It provides everything "out of the box": from DI to security.

Advantages for Kotlin

• Full support for nullable types and data classes
• Automatic conversion of Java annotations to Kotlin style
• Use of coroutines in reactive controllers
• Huge community and thousands of ready-made starters

Controller Example

@RestController@RequestMapping("/api/products")class ProductController(private val productService: ProductService) {

    @GetMapping("/{id}")    suspend fun getProduct(@PathVariable id: Long): Product {        return productService.findById(id)    }

    @PostMapping    fun createProduct(@RequestBody product: Product): Product {        return productService.save(product)    }}

3. Javalin — Lightweight and Simple

Javalin is a minimalist framework inspired by Spark and Express.js. It is ideal for small projects and prototypes.

Key Features

• No magic — everything is explicit and transparent
• Built-in support for WebSocket and OpenAPI
• Works on Java and Kotlin without changes
• No configuration files required

Routing Example

import io.javalin.Javalin

fun main() {    val app = Javalin.create { config ->        config.enableCorsForAllOrigins()    }.start(7000)

    app.get("/hello") { ctx ->        ctx.json(mapOf("message" to "Hello from Javalin!"))    }

    app.get("/users") { ctx ->        ctx.json(listOf(            mapOf("id" to 1, "name" to "Alice"),            mapOf("id" to 2, "name" to "Bob")        ))    }}

4. Vert.x — Reactive Toolkit

Vert.x is not just a framework, but a whole ecosystem for reactive programming. It supports many languages, including Kotlin.

Strengths

• Reactive event-loop (asynchrony on steroids)
• Support for clustering and distributed systems
• Built-in HTTP client and server
• Excellent integration with Kotlin Coroutines

HTTP Server Example

import io.vertx.kotlin.coroutines.*import io.vertx.core.Vertximport io.vertx.ext.web.Router

suspend fu