Krema

Build modern desktop apps with Java and your favorite web framework.

Krema is to the Java ecosystem what Tauri is to Rust — lightweight, native desktop applications powered by system webviews instead of a bundled browser. Write your backend in Java, your frontend in React/Vue/Angular/Svelte, and ship small, fast, cross-platform apps.

Getting Started · Documentation · Examples

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Why Krema?

	Electron	Tauri	Krema
Backend language	JavaScript	Rust	Java
Webview	Bundled Chromium	System	System
App size	~150 MB	~3 MB	~5 MB
Memory usage	High	Low	Low
Ecosystem	npm	Cargo	Maven + npm

Krema uses the OS-native webview (WebKit on macOS, WebView2 on Windows, WebKitGTK on Linux) and communicates with Java via Project Panama (Foreign Function & Memory API) — no JNI, no bundled browser, no Electron overhead. You get the full power of the JDK ecosystem for your backend logic, and complete freedom to use any web framework for the UI.

Features

• System Webviews — WebKit (macOS), WebView2 (Windows), WebKitGTK (Linux). No bundled browser.
• Project Panama FFI — Direct native calls via Java 25's Foreign Function & Memory API. No JNI.
• Any Frontend Framework — React, Vue, Angular, Svelte, or plain HTML/CSS/JS.
• Type-Safe IPC — Annotate Java methods with @KremaCommand and call them from the frontend with full type safety.
• Backend-to-Frontend Events — Push real-time events from Java to the UI.
• Rich Native APIs — Window management, menus, dialogs, notifications, clipboard, system tray, global shortcuts, drag & drop, secure storage, and more.
• Plugin System — Extend with official plugins (SQLite, WebSocket, file upload, window positioning, autostart) or build your own.
• Native Packaging — Bundle as native executables with GraalVM, or ship as JARs.
• Splash Screens — Built-in configurable splash screens.
• Cross-Platform — macOS (ARM64, x64), Linux (x64), Windows (x64).

Quick Start

Prerequisites

• Java 25+
• Maven 3.9+

Install the CLI

# via npm
npm install -g @krema-build/krema

# or via curl
curl -fsSL https://krema.build/install.sh | bash

Create and Run a Project

krema init my-app --template react
cd my-app
krema dev

That's it. A native window opens with your React app, backed by Java.

How It Works

Krema apps have two sides: a Java backend that handles business logic and native APIs, and a web frontend that renders the UI in a system webview. They communicate through a type-safe IPC bridge.

1. Define Commands in Java

Annotate any method with @KremaCommand to expose it to the frontend:

import build.krema.core.KremaCommand;

public class Commands {

    @KremaCommand
    public String greet(String name) {
        return "Hello, " + name + "!";
    }

    @KremaCommand
    public SystemInfo systemInfo() {
        return new SystemInfo(
            System.getProperty("os.name"),
            System.getProperty("java.version"),
            Runtime.getRuntime().availableProcessors()
        );
    }

    public record SystemInfo(String os, String javaVersion, int cpus) {}
}

2. Call Them from the Frontend

// Invoke a command and get a typed response
const greeting = await window.krema.invoke<string>('greet', { name: 'World' });

const info = await window.krema.invoke<SystemInfo>('systemInfo', {});
console.log(`Running on ${info.os} with Java ${info.javaVersion}`);

3. Wire Up the Application

import build.krema.core.Krema;

public class Main {
    public static void main(String[] args) {
        Krema.app()
            .title("My App")
            .size(1024, 768)
            .commands(new Commands())
            .devUrl("http://localhost:5173")  // points to your frontend dev server
            .run();
    }
}

4. Push Events from Java to the Frontend

// Java: emit events to the frontend
emitter.emit("timer-tick", Map.of("count", tickCount, "timestamp", System.currentTimeMillis()));

// Frontend: listen for events
window.krema.on('timer-tick', (data) => {
  console.log(`Tick #${data.count}`);
});

Configuration

Projects are configured with a krema.toml file:

[package]
name = "my-app"
version = "1.0.0"
identifier = "com.example.my-app"

[window]
title = "My App"
width = 1024
height = 768
resizable = true

[build]
frontend_command = "npm run build"
frontend_dev_command = "npm run dev"
frontend_dev_url = "http://localhost:5173"
main_class = "com.example.app.Main"

[permissions]
allow = ["clipboard:read", "clipboard:write", "notification"]

Native APIs

Krema provides built-in access to native platform features, available from both Java and the frontend:

API	Description
Window	Resize, move, minimize, maximize, fullscreen, frameless mode
Menu	Menu bar, context menus, dock menus
Dialogs	File open/save, folder picker, message boxes
Notifications	Native desktop notifications
Clipboard	Read/write text and images
System Tray	Tray icons with menus
Global Shortcuts	System-wide keyboard shortcuts
Drag & Drop	File drop handling
Secure Storage	OS keychain / credential storage
Store	Persistent key-value storage
Shell	Open URLs, reveal files in Finder/Explorer
Screen	Multi-monitor info and positioning
HTTP Client	Native HTTP requests

Plugins

Extend your app with official plugins:

<dependency>
    <groupId>build.krema</groupId>
    <artifactId>krema-plugin-sql</artifactId>
    <version>0.1.0</version>
</dependency>

Plugin	Description
krema-plugin-sql	SQLite database access
krema-plugin-websocket	WebSocket connections
krema-plugin-upload	File upload handling
krema-plugin-positioner	Window positioning (center, corners, etc.)
krema-plugin-autostart	Launch at login

Project Structure

krema/                        Core framework
  krema-core/                 Webview bindings, IPC, window management
  krema-cli/                  Command-line interface
  krema-processor/            Annotation processor for @KremaCommand
krema-plugins/                Official plugins
  krema-plugin-sql/           SQLite database access
  krema-plugin-websocket/     WebSocket connections
  krema-plugin-upload/        File upload handling
  krema-plugin-positioner/    Window positioning
  krema-plugin-autostart/     Launch-at-login
krema-demos/                  Example applications
  krema-react/                React + TypeScript demo
  krema-vue/                  Vue demo
  krema-angular/              Angular demo
krema-docs/                   Documentation site

Documentation

Full documentation is available at krema.build.

License

This project is licensed under the Business Source License 1.1.

• Change Date: 2030-02-06
• Change License: Apache License, Version 2.0

After the change date, the code becomes available under the Apache 2.0 license. See the LICENSE file for full terms.