Textual

Textual

Use when work is primarily Textual TUI, terminal workflow, or tests for Textual widgets and screens.

Boundary

Use for:

• Textual app structure and widget composition
• layout and .tcss styling
• bindings, actions, focus, interactive behavior
• screens, dialogs, menus, drawers, navigation flows
• headless functional testing with run_test()

Pair with:

• python for general Python conventions, typing, project workflow
• rich when renderables, terminal formatting, or console UX matter outside TUI
• quality when interaction regressions or state bugs need stronger tests

Reference Map

• references/app-structure.md -- app shape, widgets, reactivity, messages, screens, state boundaries
• references/widgets.md -- common widgets, tables, forms, containers, custom widget guidance
• references/widget-development.md -- custom widget patterns: base class selection, composition, lifecycle, advanced compositions
• references/layout-and-styling.md -- .tcss, containers, layout, spacing, ids, classes, visual structure, themes, colors
• references/reactive-programming.md -- reactive attrs, watchers, computed props, valid, complex state, recompose
• references/interactivity.md -- bindings, actions, focus, mouse and keyboard handling, interaction patterns
• references/testing.md -- headless tests, full Pilot API, resize, animations, workers, assert patterns for complex widgets

Assets

• assets/app.py -- small Textual app with bindings, dialog-like screen, stable selectors for tests
• assets/app.tcss -- matching .tcss file for example app
• assets/test_app.py -- headless functional tests using run_test()

What Stays Here

Keep this file focused on defaults and guardrails.

• keep here: app design defaults, testing stance, review cues
• move to refs: widget catalogs, long examples, styling details, specific test recipes
• use assets for copyable app and test skeletons over growing giant code blocks in refs

Core Defaults

• widgets small, responsibility-driven
• styling in .tcss, not large inline CSS strings
• semantic ids/classes so tests and styles have stable targets
• reactive state only for values that genuinely affect UI
• watchers small, explicit; heavy logic out of watch_* methods
• prefer action_* + BINDINGS for keyboard behavior
• messages/events explicit; no smuggling state through globals
• screens or focused containers for dialog-like flows, not one giant app class
• stable widget ids/classes so styling, querying, tests align
• prefer built-in widgets/messages before inventing custom abstractions
• test interactions headlessly with run_test() over only checking impl details
• always call super().__init__(name=name, id=id, classes=classes) in custom widget __init__
• replace list/dict entirely to trigger watchers -- .append() won't fire watch_*
• frozen dataclasses for immutable reactive data points

Quick Start

from textual.app import App, ComposeResult
from textual.widgets import Footer, Header, Label


class DemoApp(App):
    CSS_PATH = "app.tcss"
    def compose(self) -> ComposeResult:
        yield Header()
        yield Label("Hello, Textual!", id="status")
        yield Footer()


if __name__ == "__main__":
    DemoApp().run()

Testing Defaults

• use async with app.run_test() as pilot: for functional tests
• call await pilot.pause() after interactions that queue updates
• use await pilot.wait_for_animation() when animation timing matters
• use await pilot.wait_for_scheduled_animations() for all scheduled animations
• use await pilot.app.workers.wait_for_complete() for worker-driven flows
• assert both user-visible state and underlying app state when useful
• configure pytest with asyncio_mode = "auto" -- avoids @pytest.mark.asyncio on every test
• use pilot.app.query_one("#id", WidgetType) for typed querying
• test different terminal sizes with run_test(size=(w, h))

For deeper patterns, load references/testing.md.

Reactive Defaults

• declare type: attr: reactive[Type] = reactive(default)
• use init=False when initializing in __init__; omit when reactive sets default
• use recompose=True when attribute change should rebuild child widget tree
• use layout=True when attribute change affects size/position
• watcher signature: watch_attr(self, old: T, new: T) -> None
• computed: use @property for derived values; update via watcher when dependency changes
• for valid: constrain in watch_*, revert or clamp value there

For full patterns, load references/reactive-programming.md.

Widget Development Defaults

• extend Static for display-only content; extend Container/Vertical/Horizontal for composition
• put DEFAULT_CSS on class for self-contained defaults
• use keyword-only args (after *) for id, name, classes
• always pass name, id, classes to super().__init__()
• store config in _prefixed instance vars; never in class vars that aren't ClassVar
• custom messages: define as nested class; use post_message() from child, handle in parent
• messages flow UP -- parents handle, children emit; attributes flow DOWN -- parents set child attrs

For deep patterns, load references/widget-development.md.

• do not bury most of app in one monolithic App class
• do not rely on fragile widget order when ids or classes can make tests stable
• do not mix layout, styling, and interaction logic into same method
• do not overuse reactivity for one-off imperative updates
• do not make keyboard shortcuts undocumented or inconsistent with visible UI
• do not write Textual tests that only assert internal methods were called

Review Focus

• widget boundaries clear, reusable
• layout and styling targets stable
• bindings and actions discoverable, consistent
• dialogs, menus, drawers have sensible focus and close behavior
• tests cover real interaction flows, not only internal state