Textual applications

Inspect the app, locked dependencies, entry point, TCSS, tests, and actual user workflow. Choose built-in widgets and composition before custom rendering. Keep application state separate from long-running work and make keyboard paths first- class. Do not require a dashboard, mode system, or command palette for every app.

Choose a structure

A small tool can keep one App; separate Screens when the user's context changes, ModalScreen for short interruptions, ContentSwitcher for local steps, and modes for genuinely independent top-level screen stacks. Use stable IDs and semantic classes for styling and tests, with narrow-terminal layouts before wider panes. Prefer DataTable, Tree/DirectoryTree, MarkdownViewer, TextArea, and built-in input widgets when their behaviour fits. Do not split a cohesive component merely to satisfy a line-count heuristic.

Read architecture, widgets, or screens only as needed.

Responsive work and state

Read reactivity and workers before changing concurrent behaviour. Async workers share the event loop: blocking calls do not become nonblocking when wrapped in async def or @work. Use async APIs, thread=True for blocking I/O, and a suitable process/native strategy for substantial CPU work.

Exclusive cancellation is not a transaction rollback or a guarantee that a thread has stopped. Carry a request revision and check it again when applying results on the UI thread. Keep worker failure, cancellation, empty data, and successful data distinct. A cancelled remote write may still have happened.

reactive controls refresh-related state; var retains reactive features without automatic refresh/layout. Neither is a substitute for a plain field where reactive behaviour is unnecessary. Keep compute methods cheap and pure, and watchers free of blocking work. Initialise pre-mount reactive values deliberately.

Existing projects and source tools

Resolve SKILL_DIR to this installed skill directory, not the app repository. The inspect/audit helpers provide heuristic source leads, not proof of architecture, responsive runtime behaviour, or missing capabilities. Read flagged code before changing it. Do not add palette/browser/export/breakpoint machinery only to clear a heuristic warning.

dump_dom_and_bindings.py imports and runs the application under run_test; it can execute startup/network/filesystem actions. Run it only in an authorised isolated test environment with fake services and suitable configuration. It is not a passive source read. The same applies to generated Pilot tests and snapshot tooling.

Safe scaffolding

The starter templates remain available, but generation now previews by default:

python "$SKILL_DIR/scripts/scaffold_textual_app.py" --list-templates
python "$SKILL_DIR/scripts/scaffold_textual_app.py" \
  --template data-explorer --module my_app --class-name MyApp --app-title 'My App'

Review the rendered app, TCSS, and tests. To write, add --write --output-dir with a new final directory whose parent already exists. There is no force/overwrite or automatic pyproject/CI option. Free titles are inserted as AST string values, identifiers are validated, and all selected templates are parsed before any write. Generated Python is reformatted by ast.unparse, not executed. A write failure can leave a private partial draft; it is not an atomic multi-file transaction.

For the chat starter, read request ownership and tests. Its explicit Stop action, draft preservation, and late-result checks are part of the supplied example, not behaviour to infer from the worker decorator.

Integrate selected output deliberately into the app. Review packaging/CI against the existing project and current supported Python/tool versions rather than copying a new universal build system. Older standalone emit helpers are optional starting scaffolds, not a current dependency/CI policy or automatic upgrade path.

Runtime, delivery, and testing

Use the installed textual-dev CLI help for devtools/console/serve. Serving exposes a server-side app with its filesystem and service permissions; it is not a sandbox or automatic authentication boundary. Verify network binding, auth, tenant isolation, and the exact files offered for download before browser delivery. Treat user text and terminal/markup escapes as untrusted display data.

Test the changed behaviour with run_test/Pilot, including actual assertions, failure/ cancellation, focus and keyboard actions, narrow/wide sizes, and teardown. Use snapshots when visual layout is the relevant risk, not a mandatory quota for every change. Fixed sleeps are not proof a worker or layout settled; await a bounded observable state. Headless tests do not prove every real terminal/browser renders identically. Preserve the user's scroll position rather than always auto-anchoring logs when they are reading earlier content.

Report the patch, actual test commands/results, and untested terminal/browser paths. Do not claim a starter, syntactic parse, or golden screenshot proves production readiness. Keep testing, browser delivery, and packaging as targeted references.

Maintainers: python "$SKILL_DIR/scripts/self_check.py" parses all local starter outputs; python -m unittest discover -s "$SKILL_DIR/tests" -v tests the scaffold engine. Neither executes generated apps.

Sources reviewed 2026-09-13: Textual metadata, workers, reactivity, and testing.