An idiomatic GUI library inspired by Elm and based on gtk4-rs. Relm4 is a new version of relm that's built from scratch and is compatible with GTK4 and libadwaita.

Programming language: Rust
License: GNU General Public License v3.0 or later
Tags: GUI     Gtk     Gtk-rs     Elm-architecture    
Latest version: v0.4.2

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CI Matrix Relm4 on crates.io Relm4 docs Relm4 book Minimum Rust version 1.56 dependency status

An idiomatic GUI library inspired by Elm and based on gtk4-rs. Relm4 is a new version of relm that's built from scratch and is compatible with GTK4 and libadwaita.

Why Relm4

We believe that GUI development should be easy, productive and delightful.
The gtk4-rs crate already provides everything you need to write modern, beautiful and cross-platform applications. Built on top of this foundation, Relm4 makes developing more idiomatic, simpler and faster and enables you to become productive in just a few hours.

Our goals

  • โฑ๏ธ Productivity
  • โœจ Simplicity
  • ๐Ÿ“Ž Outstanding documentation
  • ๐Ÿ”ง Maintainability



Relm4 depends on GTK4: How to install GTK4.


Relm4 has two crates that extend the core functionality:

  • relm4-macros provides a widget macro that simplifies UI creation
  • relm4-components is a collections of reusable components you can easily integrate into your application

To use all features, just add this to your Cargo.toml:

relm4 = { version = "0.4", features = ["macros"] }
relm4-components = "0.4"


The relm4 crate has four feature flags:

 Flag  Purpose
 macros  Enable macros by re-exporting relm4-macros
 tokio-rt  Adds the AsyncRelmWorker type that uses an asynchronous update function
 libadwaita  Improved support for libadwaita
 all  Enable all features


Several example applications are available at [relm4-examples/](relm4-examples/).

[๐Ÿ“ธ Screenshots from the example apps](assets/screenshots)

A simple counter app

[Simple app screenshot light](assets/screenshots/simple-light.png) [Simple app screenshot dark](assets/screenshots/simple-dark.png)

use gtk::prelude::{BoxExt, ButtonExt, GtkWindowExt, OrientableExt};
use relm4::{send, AppUpdate, Model, RelmApp, Sender, WidgetPlus, Widgets};

struct AppModel {
    counter: u8,

enum AppMsg {

impl Model for AppModel {
    type Msg = AppMsg;
    type Widgets = AppWidgets;
    type Components = ();

impl AppUpdate for AppModel {
    fn update(&mut self, msg: AppMsg, _components: &(), _sender: Sender<AppMsg>) -> bool {
        match msg {
            AppMsg::Increment => {
                self.counter = self.counter.wrapping_add(1);
            AppMsg::Decrement => {
                self.counter = self.counter.wrapping_sub(1);

impl Widgets<AppModel, ()> for AppWidgets {
    view! {
        gtk::ApplicationWindow {
            set_title: Some("Simple app"),
            set_default_width: 300,
            set_default_height: 100,
            set_child = Some(&gtk::Box) {
                set_orientation: gtk::Orientation::Vertical,
                set_margin_all: 5,
                set_spacing: 5,

                append = &gtk::Button {
                    set_label: "Increment",
                    connect_clicked(sender) => move |_| {
                        send!(sender, AppMsg::Increment);
                append = &gtk::Button {
                    set_label: "Decrement",
                    connect_clicked(sender) => move |_| {
                        send!(sender, AppMsg::Decrement);
                append = &gtk::Label {
                    set_margin_all: 5,
                    set_label: watch! { &format!("Counter: {}", model.counter) },

fn main() {
    let model = AppModel::default();
    let app = RelmApp::new(model);


Licensed under either of

at your option.


Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.

Feedback and contributions are highly appreciated!

*Note that all licence references and agreements mentioned in the Relm4 README section above are relevant to that project's source code only.