feature-theme

A set of project rules for adding dark and light themes to a Flutter app. It covers saving the theme choice, restoring it at startup, reacting to changes, and previewing a theme without saving it.

In plain words
What is it for?
Use it when implementing theme switching, theme persistence, reset-to-system behavior, or widgets that respond to the current theme.
Why use it?
It shows what theme features already exist and which ones are not supported, reducing duplicate or incompatible code.

Cursor rule for Cursor

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add rules/sampaio-tech/flutter-core-modules/feature-theme
Clone the repo
git clone --depth 1 https://github.com/sampaio-tech/flutter-core-modules

Made for: Cursor.

Per session 0 Nothing until a file matches its globs; then the whole rule loads.
When invoked 1,231 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00000 $0.01231
Opus 5 $0.00000 $0.00616
Sonnet 5 $0.00000 $0.00246
Haiku 4.5 $0.00000 $0.00123

Measured yesterday against content hash d9c2a23e1a45, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

feature-theme scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured yesterday.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.cursor/rules/feature-theme.mdc · 154 lines

How it starts

The opening of the file, as written. The whole thing — 154 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Feature: Theme — Rules

What Is Already Implemented — Check Before Building

Capability Status
Persist dark/light theme preference SetThemeDataUsecase
Restore theme on app start (sync read) ThemeStateNotifier constructor
Reactive theme updates across app themeStateNotifierProvider (non-autoDispose)
Reset to system theme RemoveThemeDataUsecase / notifier.removeThemeData()
Preview theme without saving notifier.setThemeData(save: false)
Dark/Light mode toggle row widget ThemeRowWidget
System theme detection ❌ Not in package — use MediaQuery.platformBrightnessOf(context) when state is null
Multiple custom themes beyond light/dark ❌ Only IosLightThemeData / IosDarkThemeData supported

Before adding theme code, verify whether the above already satisfies the requirement.


Layer Structure

lib/src/features/theme/
├── domain/
│   ├── repositories/theme_repository.dart          # abstract ThemeRepository
│   └── usecases/
│       ├── get_theme_data_usecase.dart
│       ├── set_theme_data_usecase.dart
│       └── remove_theme_data_usecase.dart
├── data/
│   └── repositories/theme_repository.dart          # ThemeRepositoryImpl + provider
└── presentation/
    └── notifiers/
        └── theme_state_notifier.dart               # ThemeStateNotifier + themeStateNotifierProvider

Wiring Theme to the App Root

class MyApp extends HookConsumerWidget {
  @override
  Widget build(BuildContext context, WidgetRef ref) {
    final themeData = ref.watch(themeStateNotifierProvider); // IosThemeData?

    return IosTheme(
      data: themeData ?? IosLightThemeData(), // null = fallback to light
      child: CupertinoApp(
        theme: CupertinoThemeData(
          brightness: switch (themeData) {
            null                => Brightness.light,
            IosLightThemeData() => Brightness.light,
            IosDarkThemeData()  => Brightness.dark,
          },
        ),
      ),
    );
  }
}

Read the full file on GitHub · 154 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. yesterday First seen · 154 lines · 0 tokens per session scan A d9c2a23e1a45

Subscribe to this mod's changes

feature-theme is a cursor rule published in the GitHub repository sampaio-tech/flutter-core-modules (2 stars, last pushed 10d ago), licensed MIT. It costs nothing until one of its globs matches a file; then it loads 1,231 tokens. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.