Tesserae

Write desktop apps in Python and YAML. A Tesserae app is YAML views (what the screen looks like), each paired with a Python ViewModel (what it does), drawn by the Tesserae Render Engine (tre): rendering, layout, animation and accessibility in Rust underneath, which you never have to touch.

# Counter_View.yaml
id: root
kind: Container
style: {flex_direction: vertical, gap: 12, padding: 24, background: surface}
children:
  - id: label
    kind: Text
    text: {content: "Count: 0", typography_role: headline_medium}
    style: {foreground: on_surface}
    bindings: {text: "{{ label_text.get() }}"}
  - id: button
    component: ButtonFilled
    with: {label: Count, width: 120, height: 40, corner_radius: 20}
    handlers: {on_click: increment}

# Counter_ViewModel.py
from tesserae import Computed, Signal, ViewModel

class CounterViewModel(ViewModel):
    def __init__(self, view):
        self.count = Signal(0)
        self.label_text = Computed(lambda: f"Count: {self.count.get()}")
        super().__init__(view)

    def increment(self):
        self.count.update(lambda n: n + 1)

# app.py
from tesserae import App
from Counter_ViewModel import CounterViewModel

app = App(width=240, height=160, title="Counter")
app.load("Counter_View.yaml", CounterViewModel)
app.show("Counter")
app.run(hot_reload=True)   # edit the view while the app runs

Tesserae is on PyPI as tesserae-ui, pre-alpha, and runs on Linux, macOS and Windows.

What you get

• Screens and components. An App owns the window and a registry of screens; a screen is a view and ViewModel pair, checked by naming convention. Embed other pairs as components, or reuse structure as fragments.
• Reactive state. Signal, Computed, Effect and ViewModel: bindings keep the screen in step with them. See Reactivity and Repeater.
• Material Design 3. Every MD3 component with its YAML, a stylesheet for each, and themes: a seed colour makes the palette, and light and dark follow the OS.
• Real desktop behaviour. Keyboard, state layers and screen-reader support, overlays, a window, docks and embedded views, and custom title bars.
• Fast iteration. Hot reload updates a running app when a view, a stylesheet or a theme changes, and editor support completes and checks your YAML.
• Shipping. tesserae build makes one executable, or an installer: Releasing.

Where to go

Installation	pip install tesserae-ui
Getting Started	Your first window and node, declaratively and from Python
Tutorial and the same as a project	A Tasks app in six steps: components, styling, screens, a custom window; in one flat folder, then as a tesserae new project
Guide	How each part works
Components and Stylesheets	Every MD3 component, its YAML and its look
Themes	Colour, shape, type, light and dark
Python API and YAML reference	Every class, function and key
Architecture	How it fits together
Changelog and Migrating	What changed, release by release

Files: Tesserae reads them, tre gets data

You always give Tesserae file paths: views, fragments, include:d files, images, themes, stylesheets and fonts. Tesserae reads, parses, decodes and watches them itself and hands tre only data. Every error names the file you wrote, and a view and everything it is built from can be hot-reloaded.