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Building RESTful APIs with Ktor

Harsh Vardhan
Harsh Vardhan
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Ktor is a lightweight, asynchronous web framework that makes it easy to create high-performance RESTful APIs. Building RESTful APIs using Ktor is a great choice for Kotlin developers. In this blog, we’ll see how we can build a simple RESTful API using Ktor. Let’s get started:


  1. Basic knowledge of Kotlin programming language
  2. JDK (Java Development Kit) installed
  3. A code editor (e.g., IntelliJ IDEA, Visual Studio Code)
  4. cURL or Postman for testing the API endpoints
Step 1. Go to and from there generate a new ktor project and add routing plugin. It will download a sample ktor project for you.
Step 2. Add the following dependency in your project
Step 3. Application.kt is the main entry point of our application
Step 4. Define Data Model given as below, for example we’re taking a ToDo app data model.
data class Todo(val id: Int, val title: String, val completed: Boolean)
Step 5: Implement the API Endpoints

define the API endpoints under the routing block, and also define in memory storage list before it.

val todos = mutableListOf<Todo>()
var currentId = 1

routing {
    route("/todos") {
        get {
        get("/{id}") {
            val id = call.parameters["id"]?.toIntOrNull()
            val todo = todos.find { == id }
            if (todo != null) {
            } else {
        post {
            val todo = call.receive<Todo>()
            val newTodo = todo.copy(id = currentId++)
            call.respond(HttpStatusCode.Created, newTodo)
        put("/{id}") {
            val id = call.parameters["id"]?.toIntOrNull()
            val todoIndex = todos.indexOfFirst { == id }
            if (todoIndex != -1) {
                val updatedTodo = call.receive<Todo>()
                todos[todoIndex] = updatedTodo.copy(id = id!!)
                call.respond(HttpStatusCode.OK, updatedTodo)
            } else {
        delete("/{id}") {
            val id = call.parameters["id"]?.toIntOrNull()
            if (todos.removeIf { == id }) {
            } else {
Step 6. Run the Application

Run the main function in your Application.kt file.

Step 7. Test the Endpoints

Use tools like Postman or cURL to test your API endpoints:

  • Create a new Todo item:
    POST http://localhost:8080/todos

similarly, We can test other end points.


In conclusion, building RESTful APIs with Ktor offers a powerful and efficient solution for developing web applications in Kotlin. Throughout this blog post, we explored the fundamental steps involved in creating a RESTful API using Ktor, along with a practical example of building a Todo List API.

If you’re new to kotlin, you can explore about kotlin from here!

Harsh Vardhan

Harsh Vardhan

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