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  1. What is Kweb?
  2. Features
  3. How does it work?
  4. What does it look like?

What is Kweb?

Kweb is a library for building web applications in the Kotlin programming language.

Kweb is fairly unusual in that, while your code runs on the server, Kweb allows you to interact to the browser DOM directly as if it was local to the web server.

For example, here we create a <p> element and set its text:

doc.body.p().text("this is an example HTML paragraph")

You can also interact to JavaScript directly, although you should rarely need to do this:

doc.body.execute("console.log((new Date()).getDay());")

You can even query JavaScript and do something to the result:

val day = doc.body.evaluate("$('#day').text()")
database.update(BOOK).set(BOOK.DAY, day).execute()

Kweb has plugins for JavaScript libraries like JQuery and others. It’s also surprisingly easy to build your own plugins for other JavaScript libraries, or extend those Kweb already supports.

status experimental

Kweb is currently experimental, please play with it, give us feedback, join our development effort, but remember that it is still a few months away (June 2017) from being suitable for non-experimental use.


  • Build websites in Kotlin
  • Makes the barrier between web-browser and web-server largely invisible to the programmer
  • Seamlessly integrates with powerful JavaScript libraries like JQuery, Semantic-UI, and others
  • Update your web browser instantly in response to code changes
  • Bind DOM elements in the browser directly to persistent state on the server and have them update automatically, through the observer and data mapper patterns, and following the single source of truth principle)
  • Easy to add to an existing project, Kweb is just a library, it doesn’t seek to tell you how your project should be organized

How does it work?

Kweb keeps all of the logic server-side, and uses efficient websockets to communicate to web browsers. We also take advantage of Kotlin’s powerful new coroutines mechanism to efficiently handle asynchronicity, largly invisibly to the programmer.

What does it look like?

Here we create a simple “todo” list app:

fun main(args: Array<String>) {
    Kweb(8091, debug = true) { {
            h1().text("Simple Kweb demo - a to-do list")
            p().text("Edit the text box below and click the button to add the item.  Click an item to remove it.")

            val ul = ul().new {
                for (text in listOf("one", "two", "three")) {

            val inputElement = input(type = InputType.text, size = 20)
            button().apply {
                text("Add Item")
                    future {
                        val newItemText = inputElement.getValue().await()

fun ElementCreator<ULElement>.newListItem(text: String) {
    li().apply {
        text(text) {

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