HTTP Client for Kotlin: Top Libraries

HTTP Client for Kotlin: Top Libraries for Network Operations

Kotlin is a modern language actively used for both Android development and server-side applications. Regardless of the application domain, almost any project requires interaction with remote APIs. Choosing the right HTTP client critically impacts performance, code readability, and maintainability. In this article, we will review the best libraries for working with HTTP in Kotlin, their features, and usage examples.

1. Ktor Client — The Official Choice from JetBrains

Ktor Client is a multiplatform HTTP client from the creators of Kotlin. It supports JVM, Android, iOS, JavaScript, and Native. The main advantage is built-in asynchronicity and full integration with Kotlin coroutines.

// build.gradle.ktsimplementation("io.ktor:ktor-client-core:2.3.7")implementation("io.ktor:ktor-client-cio:2.3.7") // engine for JVM

// Simple GET requestimport io.ktor.client.*import io.ktor.client.request.*import io.ktor.client.statement.*

suspend fun fetchData(): String {    val client = HttpClient()    val response: HttpResponse = client.get("https://api.example.com/data")    return response.bodyAsText()}

Pros:

Full multiplatform support
Native coroutine support
Modular architecture (engines: CIO, OkHttp, Android, Jetty)
Built-in serialization via kotlinx.serialization

Cons:

Requires more code for simple scenarios
Fewer third-party plugins compared to OkHttp

2. OkHttp — A Time-Tested Standard

OkHttp is one of the most popular libraries in the Java/Kotlin ecosystem. Developed by Square. It is known for high performance, automatic redirect handling, caching, and HTTP/2 support.

// build.gradle.ktsimplementation("com.squareup.okhttp3:okhttp:4.12.0")

// GET request with OkHttpimport okhttp3.OkHttpClientimport okhttp3.Request

fun getData(): String {    val client = OkHttpClient()    val request = Request.Builder()        .url("https://api.example.com/data")        .build()        client.newCall(request).execute().use { response ->        return response.body?.string() ?: ""    }}

Pros:

Maximum performance
Huge community and documentation
Integration with Retrofit and Picasso
WebSocket and SSE support

Cons:

Synchronous API by default (requires coroutines or RxJava for asynchronicity)
Not multiplatform (JVM/Android only)

3. Retrofit — Declarative REST Client

Retrofit from Square is not just an HTTP client, but a whole framework for working with REST APIs. It allows you to describe endpoints through interfaces with annotations, making the code clean and predictable.

// build.gradle.ktsimplementation("com.squareup.retrofit2:retrofit:2.9.0")implementation("com.squareup.retrofit2:converter-gson:2.9.0")

// API interfaceinterface ApiService {    @GET("users/{id}")    suspend fun getUser(@Path("id") userId: Int): User}

// Usageval retrofit = Retrofit.Builder()    .baseUrl("https://api.example.com/")    .addConverterFactory(GsonConverterFactory.create())    .build()

val service = retrofit.create(ApiService::class.java)val user = service.getUser(42)

Pros: