Ktor Client for Kotlin: Complete Guide with Examples

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Ktor Client is a powerful, lightweight, and multiplatform library for making HTTP requests in Kotlin. Developed by JetBrains, it is part of the Ktor ecosystem and provides an asynchronous, coroutine-oriented API for interacting with web servers. Unlike many other HTTP clients, Ktor Client is natively designed to work on multiple platforms: JVM, Android, iOS, macOS, Linux, Windows, and JavaScript (via Kotlin/JS). This makes it an ideal choice for developing cross-platform applications with Kotlin Multiplatform (KMP).

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Why do you need Ktor Client? In modern development, almost no application can function without interacting with remote APIs. Whether it's loading data from a REST service, submitting forms, uploading files, or working with WebSockets — an HTTP client is a fundamental tool. Ktor Client offers not just basic GET and POST request capabilities, but a whole ecosystem of plugins (or "engines") that allow you to configure serialization (JSON, XML, Protobuf), compression, logging, authentication, retries, and much more. Its main advantage is full asynchronicity based on Kotlin coroutines, which ensures high performance and concise code without callbacks.

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The library features a modular architecture. You only include the components that your project actually needs: the base client, a specific engine (e.g., OkHttp for Android/JVM or Darwin for iOS), a serializer, and necessary plugins. This minimizes the final application size and avoids dependency conflicts. Ktor Client is actively developed, has excellent documentation, and is supported by the Kotlin community.

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Installation

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Ktor Client is distributed via the Gradle (or Maven) build system. Since it is not a Python package, the pip install command is not used. Below are precise instructions for adding dependencies to your build.gradle.kts file.

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Important: Library versions must be compatible. It is recommended to use the latest stable version from the official Maven Central repository. At the time of writing, the current version is 2.3.12.

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// build.gradle.kts (Gradle Kotlin DSL)\n\n// 1. Add the repository (usually already present)\nrepositories {\n    mavenCentral()\n}\n\n// 2. Add dependencies in the dependencies block\ndependencies {\n    // Base client (required)\n    implementation("io.ktor:ktor-client-core:2.3.12")\n\n    // Engine - choose one of the options:\n    // For JVM (uses Java HttpClient or OkHttp)\n    implementation("io.ktor:ktor-client-okhttp:2.3.12") // Recommended for Android/JVM\n    // implementation("io.ktor:ktor-client-java:2.3.12") // Alternative for JVM\n\n    // For iOS/macOS (native Darwin)\n    // implementation("io.ktor:ktor-client-darwin:2.3.12")\n\n    // For JavaScript\n    // implementation("io.ktor:ktor-client-js:2.3.12")\n\n    // For Windows/Linux (Curl)\n    // implementation("io.ktor:ktor-client-curl:2.3.12")\n\n    // Plugins (optional, but very useful):\n    // JSON serialization (Gson or Kotlinx Serialization)\n    implementation("io.ktor:ktor-client-content-negotiation:2.3.12")\n    implementation("io.ktor:ktor-serialization-gson:2.3.12")\n    // or implementation("io.ktor:ktor-serialization-kotlinx-json:2.3.12")\n\n    // Logging\n    implementation("io.ktor:ktor-client-logging:2.3.12")\n\n    // For working with WebSockets\n    // implementation("io.ktor:ktor-client-websockets:2.3.12")\n}\n

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If you use Maven, the dependencies will look similar. After adding the dependencies, synchronize the project (Sync Project with Gradle Files).

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