Agent Tui Expert

Agent TUI Expert

Expert guidance for building professional Terminal User Interfaces in Python.

CRITICAL: WSL2 Users Read First

If developing in WSL2, read @references/wsl2-platform-issues.md BEFORE starting.

WSL2 has a critical bug (Microsoft/WSL#1001) where horizontal terminal resize does not propagate SIGWINCH signals. This breaks Textual resize handling and requires a specific workaround using ioctl TIOCGWINSZ polling. The reference file contains tested workarounds for these issues.

When to Use This Skill

• Building full-screen TUI applications with multiple panes
• Creating IDE-like layouts (file tree, editor, terminal)
• Adding command input with history and auto-completion
• Building interactive REPLs or shell interfaces
• Implementing keyboard navigation and shortcuts
• Testing TUI applications with automated interactions

Decision Tree

Need multi-pane, full-screen UI?
├─ YES → Use Textual
│        (widgets, containers, CSS styling, message passing)
│
Need advanced line editing, history, completions?
├─ YES → Use Prompt Toolkit
│        (PromptSession, FileHistory, Completers, key bindings)
│
Need both?
└─ Use Textual with Suggester API for input completion
   Or embed prompt_toolkit patterns in custom widgets

Quick Reference

Textual Minimal App

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

class MyApp(App):
    CSS = """
    Screen { align: center middle; }
    #content { border: solid $primary; padding: 1 2; }
    """
    BINDINGS = [("q", "quit", "Quit"), ("d", "toggle_dark", "Dark Mode")]

    def compose(self) -> ComposeResult:
        yield Header()
        yield Static("Hello, Textual!", id="content")
        yield Footer()

    def action_toggle_dark(self) -> None:
        self.dark = not self.dark

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

Prompt Toolkit Minimal Prompt

from prompt_toolkit import PromptSession
from prompt_toolkit.history import FileHistory
from prompt_toolkit.completion import WordCompleter

session = PromptSession(
    history=FileHistory(".history"),
    completer=WordCompleter(["help", "quit", "status", "run"]),
)

while True:
    text = session.prompt(">>> ")
    if text == "quit":
        break
    print(f"You entered: {text}")

Contents Index

References (Detailed Documentation)

Examples (Canonical Code)

Tests (Exemplar Patterns)

Textual Key Concepts

App Lifecycle

• compose() - Build widget tree (yields widgets)
• on_mount() - Called when app starts
• on_ready() - Called when app is ready for input

Containers

• Horizontal - Left-to-right layout
• Vertical - Top-to-bottom layout
• Container - Generic wrapper
• Grid - Grid layout with grid-size, grid-columns

CSS Styling

Screen { background: $surface; }
#sidebar { dock: left; width: 25; }
.highlight { background: $accent; }
Widget:focus { border: thick $success; }

Messages

class MyWidget(Static):
    class Changed(Message):
        def __init__(self, value: str) -> None:
            self.value = value
            super().__init__()

    def update_value(self, value: str) -> None:
        self.post_message(self.Changed(value))

# In App:
def on_my_widget_changed(self, message: MyWidget.Changed) -> None:
    self.log(f"Changed to: {message.value}")

Key Bindings

BINDINGS = [
    ("q", "quit", "Quit"),
    ("ctrl+s", "save", "Save"),
    ("ctrl+p", "command_palette", "Commands"),
]

def action_save(self) -> None:
    # Handle save
    pass

Themes

Use built-in themes for professional styling out of the box:

class MyApp(App):
    theme = "textual-dark"  # or "nord", "gruvbox", "tokyo-night"

Theme variables: $primary, $surface, $text, $accent, $warning, $error, $success

Shade variations: $primary-lighten-1, $primary-darken-2, etc.

See @references/themes-and-colors.md for full details.

Prompt Toolkit Key Concepts

History

from prompt_toolkit.history import FileHistory, InMemoryHistory

# Persistent across sessions
history = FileHistory("~/.myapp_history")

# In-memory only
history = InMemoryHistory()

Completions

from prompt_toolkit.completion import WordCompleter, NestedCompleter

# Simple word list
completer = WordCompleter(["red", "green", "blue"])

# Nested commands
completer = NestedCompleter.from_nested_dict({
    "show": {"status": None, "config": None},
    "set": {"verbose": {"on": None, "off": None}},
})

Key Bindings

from prompt_toolkit.key_binding import KeyBindings

bindings = KeyBindings()

@bindings.add("c-x")
def exit_handler(event):
    event.app.exit()

session = PromptSession(key_bindings=bindings)

Validation

from prompt_toolkit.validation import Validator

validator = Validator.from_callable(
    lambda text: text.isdigit(),
    error_message="Must be a number",
)
text = prompt("Number: ", validator=validator)

Testing Quick Reference

Textual Pilot API

import pytest
from my_app import MyApp

@pytest.mark.asyncio
async def test_button_click():
    app = MyApp()
    async with app.run_test() as pilot:
        await pilot.click("#my-button")
        assert app.query_one("#result").renderable == "Clicked!"

Snapshot Testing

def test_app_snapshot(snap_compare):
    assert snap_compare("path/to/app.py", press=["tab", "enter"])

Integration Quick Reference

MCP Server Access

class MyApp(App):
    def __init__(self, mcp_client: Any) -> None:
        super().__init__()
        self.mcp_client = mcp_client

    async def load_data(self) -> None:
        result = await self.mcp_client.call_tool(
            "database_query",
            {"query": "SELECT * FROM items"}
        )
        # Update widgets with result

Sub-Agent Delegation

async def on_input_submitted(self, event: Input.Submitted) -> None:
    async for chunk in self.agent_client.run_task(event.value):
        self.query_one("#output", RichLog).write(chunk.content)

See @references/integration-patterns.md and @references/workflow-examples.md for complete examples.

Version Requirements

• Python >= 3.12
• Textual >= 1.0.0
• prompt-toolkit >= 3.0.52
• pytest >= 9.0.1
• pytest-asyncio >= 1.2.0
• pytest-textual-snapshot >= 1.1.0

Resources

• Textual Documentation
• Textual Widget Gallery
• Textual Testing Guide
• Textual Design Guide - Themes and variables
• Textual Color Reference - Color formats
• Prompt Toolkit Documentation
• Prompt Toolkit GitHub