Compose Expert Skill for Claude

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> This banner will remain through v2.x and escalate in v3.0.

When this skill applies

The frontmatter description: is intentionally short to satisfy Codex / Copilot

CLI's 1024-character cap on that field (see issue #12). The full trigger surface

lives here so it stays available to Claude after the skill loads.

Compose API mentions

@Composable, remember, mutableStateOf, derivedStateOf, rememberSaveable,

LaunchedEffect, DisposableEffect, SideEffect, rememberCoroutineScope,

Scaffold, NavHost, NavController, MaterialTheme, ColorScheme,

Typography, LazyColumn, LazyRow, LazyVerticalGrid, HorizontalPager,

Modifier, Modifier.Node, recomposition, CompositionLocal, Style,

styleable, MutableStyleState, Material 3 Expressive, M3 Expressive,

MaterialExpressiveTheme, ButtonGroup, SplitButton,

FloatingActionButtonMenu, LoadingIndicator, HorizontalFloatingToolbar,

NavDisplay, NavKey, rememberNavBackStack, NavigableListDetailPaneScaffold.

Compose Multiplatform / KMP

Compose Multiplatform, CMP, KMP, commonMain, expect, actual,

ComposeUIViewController, Window composable, UIKitView, ComposeViewport,

Res.drawable, Res.string, SkikoMain.

Android TV

tv-material, tv-foundation, Carousel, NavigationDrawer (TV),

D-pad, focus indication, FocusRequester on TV, 10-foot UI,

living room, tv compose, Android TV, Google TV, leanback migration.

Paging 3

PagingSource, Pager, PagingConfig, PagingData, LazyPagingItems,

collectAsLazyPagingItems, RemoteMediator, LoadState,

asSnapshot, TestPager, cachedIn.

Design system / design-to-code

atomic design, atoms, molecules, organisms, templates,

design tokens, design system, component library, reusable component,

Figma to Compose, design to compose, build this UI, implement this design,

spec to code, redline.

Casual phrasing

"my compose screen is slow", "my recomposition is broken",

"how do I pass data between screens", "how do I build a TV app",

"Android UI", "Kotlin UI", "compose layout", "compose navigation",

"compose animation", "compose styles", "desktop compose", "iOS compose",

"compose web".

Review Mode triggers

Any GitHub PR URL matching github.com/.*/pull/\d+, or phrases:

"review this PR", "review this diff", "review this code",

"check this code", "check this diff", "what's wrong with this".

On match, follow references/pr-review.md exclusively.

Session start

Auto-detect Compose projects on session_start — see references/auto-init.md.

Quick Routing

Use this table first. Match the user's signal to one reference file and read it before

answering. source-code/ files are supporting evidence — load a references/*.md file

first, then cite source-code/ for implementation proof when receipts matter.

State, recomposition, side effects

• remember, rememberSaveable, mutableStateOf vs mutableIntStateOf, state hoisting → references/state-management.md
• derivedStateOf, snapshotFlow, StateFlow in UI, recomposition scope boundaries → references/state-management.md (secondary: references/performance.md)
• LaunchedEffect, SideEffect, DisposableEffect, rememberUpdatedState, rememberCoroutineScope → references/side-effects.md
• Recomposition frequency, "my screen recomposes too often", stability, @Stable/@Immutable, Compose compiler metrics, baseline profiles, strong skipping → references/performance.md
• CompositionLocal, ambient values, theming propagation, LocalContext misuse, custom locals → references/composition-locals.md

Animation and motion

• animate*AsState, AnimatedVisibility, Crossfade, updateTransition, Animatable, rememberInfiniteTransition → references/animation.md
• Shared element transitions, gesture-driven animation, Modifier.graphicsLayer, Canvas drawing, custom motion spec → references/animation.md (secondary: references/modifiers.md for graphicsLayer)
• M3 motion tokens, MotionTokens, MotionScheme, animation duration tokens, M3 easing curves → references/material3-motion.md

Layout, lists, modifiers

• LazyColumn, LazyRow, LazyVerticalGrid, LazyHorizontalGrid, key/itemKey, contentType, LazyListState, scroll state, sticky headers → references/lists-scrolling.md
• HorizontalPager, VerticalPager, PagerState → references/lists-scrolling.md
• Modifier chain ordering, custom layout, Layout, SubcomposeLayout, layout modifier, draw modifier, Painter, Modifier.Node → references/modifiers.md

Navigation

• NavHost, NavController, back stack, deep links, type-safe @Serializable routes, navigation graph, nested graphs → references/navigation.md
• Migrating from Nav 2 to Nav 3, NavDisplay, NavKey, rememberNavBackStack, NavBackStackEntry changes → references/navigation-migration.md
• Choosing between Nav 2 and Nav 3, type-safe navigation decision, KMP navigation → references/navigation-migration.md (secondary: references/navigation.md)
• Advanced Nav 3: returning results between destinations, auth-gated/conditional navigation, animated/shared-element transitions in NavDisplay, adaptive list-detail (NavigableListDetailPaneScaffold), multiple/per-tab back stacks → references/navigation-migration.md

Paging

• PagingSource, PagingData, Pager setup, PagingConfig, pagingDataFlow, invalidation → references/paging.md
• LazyPagingItems, collectAsLazyPagingItems, itemKey, itemContentType, LoadState in UI, retry/refresh → references/paging.md
• RemoteMediator, offline-first paging, network + cache paging, loadState.source.refresh → references/paging-offline.md
• Paging with MVI, dual-flow pattern, paging tests (asSnapshot, TestPager), CombinedLoadStates, paging anti-patterns → references/paging-mvi-testing.md

Theming and design systems

• MaterialTheme, ColorScheme, Typography, Shapes, dynamic color, M3 tokens, color roles → references/theming-material3.md
• Material 3 Expressive, MaterialExpressiveTheme, ButtonGroup, SplitButton, FloatingActionButtonMenu, LoadingIndicator (wavy), HorizontalFloatingToolbar, @ExperimentalMaterial3ExpressiveApi → references/theming-material3.md (motion: references/material3-motion.md)
• Atom, molecule, organism, template, component hierarchy, design system structure, reusable components, design tokens → references/atomic-design.md
• Figma → Compose, screenshot → composable, design token translation, spec-to-code, redline interpretation → references/design-to-compose.md
• Style {}, MutableStyleState, Modifier.styleable() (experimental Foundation Styles API) → references/styles-experimental.md

Multiplatform and platform-specific

• iOS/Desktop/Web CMP targets, expect/actual, commonMain, Res.drawable, Res.string, platform-specific composables → references/multiplatform.md
• ComposeUIViewController (iOS), Window/Tray/MenuBar (Desktop), UIKitView, ComposeViewport (Web), platform interop → references/platform-specifics.md
• TV Compose, androidx.tv, D-pad focus, FocusRequester on TV, Carousel, NavigationDrawer (TV), 10-foot UI, leanback migration → references/tv-compose.md

Interop and accessibility

• Compose inside XML, AndroidView, ComposeView, AbstractComposeView, hybrid migration, View → Compose interop → references/view-composition.md
• Accessibility, Modifier.semantics, TalkBack, touch target size, contentDescription, WCAG, traversal order → references/accessibility.md

Production, review, migration

• Production crash, ANR, Compose stack trace, remember leak, zero-size DrawScope, duplicate keys, stale derivedStateOf → references/production-crash-playbook.md
• PR review, code review, "review this diff", composable anti-patterns, smell detection, GitHub PR URL → references/pr-review.md
• Deprecated Compose API, "removed in version X", migration from old API, replaced symbols → references/deprecated-patterns.md
• Experimental opt-in, @OptIn, @ExperimentalFoundationStyleApi, unstable API usage → references/styles-experimental.md (for Styles); for general guidance, the relevant topic file
• Session start, project detection, auto-init → references/auto-init.md

Source-code receipts (cite, don't route to)

• "Show me the actual implementation", "where in androidx is this", internal Compose mechanics → load the topic reference first, then cite the matching references/source-code/*.md file:
• Runtime/state internals (Composer, Snapshot, Effects, Remember) → references/source-code/runtime-source.md
• UI/layout/measurement/draw internals → references/source-code/ui-source.md
• Foundation (LazyList, Pager, Clickable, Scrollable, BasicTextField) → references/source-code/foundation-source.md
• Material3 components → references/source-code/material3-source.md
• Navigation Compose internals → references/source-code/navigation-source.md
• CMP entry points (Window, ComposeUIViewController, UIKitView, ComposeViewport) → references/source-code/cmp-source.md

Compose Expert Skill

Non-opinionated, practical guidance for writing correct, performant Compose code —

across Android, Desktop, iOS, and Web. Covers Jetpack Compose and Compose Multiplatform.

Backed by analysis of actual source code from androidx/androidx and

JetBrains/compose-multiplatform-core.

Review Mode

Activate when the input contains a GitHub PR URL (github.com/.+/pull/\d+) or

explicit review phrases: "review this PR", "review this diff", "check this code",

"what's wrong with this".

When Review Mode activates:

• Do not follow the generation workflow below
• Read references/pr-review.md and follow its workflow exclusively
• Output a structured local review report — do not post to GitHub

Workflow

When helping with Compose code, follow this checklist:

1. Understand the request

• What Compose layer is involved? (Runtime, UI, Foundation, Material3, Navigation)
• Is this a state problem, layout problem, performance problem, or architecture question?
• Is this Android-only or Compose Multiplatform (CMP)?

2. Analyze the design (if visual reference provided)

• If the user shares a Figma frame, screenshot, or design spec, consult references/design-to-compose.md
• Decompose the design into a composable tree using the 5-step methodology
• Map design tokens to MaterialTheme, spacing to CompositionLocals
• Identify animation needs and consult references/animation.md for recipes

3. Consult the right reference

Read the relevant reference file(s) from references/ before answering:

| Topic | Reference File |

|-------|---------------|

| @State, remember, mutableStateOf, state hoisting, derivedStateOf, snapshotFlow | references/state-management.md |

| Structuring composables, slots, extraction, preview | references/view-composition.md — for design system structure, also see references/atomic-design.md |

| Modifier ordering, custom modifiers, Modifier.Node | references/modifiers.md |

| LaunchedEffect, DisposableEffect, SideEffect, rememberCoroutineScope | references/side-effects.md |

| CompositionLocal, LocalContext, LocalDensity, custom locals | references/composition-locals.md |

| LazyColumn, LazyRow, LazyGrid, Pager, keys, content types | references/lists-scrolling.md |

| NavHost, type-safe routes, deep links, shared element transitions | references/navigation.md |

| animate*AsState, AnimatedVisibility, Crossfade, transitions | references/animation.md — for M3 token selection, also see references/material3-motion.md |

| MaterialTheme, ColorScheme, dynamic color, Typography, shapes | references/theming-material3.md — for motion, see references/material3-motion.md; for design tokens, see references/atomic-design.md |

| Recomposition skipping, stability, baseline profiles, benchmarking | references/performance.md |

| Semantics, content descriptions, traversal order, testing | references/accessibility.md |

| Removed/replaced APIs, migration paths from older Compose versions | references/deprecated-patterns.md |

| Styles API (experimental): Style {}, MutableStyleState, Modifier.styleable() | references/styles-experimental.md |

| Figma/screenshot decomposition, design tokens, spacing, modifier ordering | references/design-to-compose.md |

| Production crash patterns, defensive coding, state/performance rules | references/production-crash-playbook.md |

| Compose Multiplatform, expect/actual, resources (Res.*), migration | references/multiplatform.md |

| Desktop (Window, Tray, MenuBar), iOS (UIKitView), Web (ComposeViewport) | references/platform-specifics.md |

| TV Compose: Surface, Carousel, NavigationDrawer, Cards, focus, D-pad | references/tv-compose.md |

| M3 motion tokens, MotionTokens, MotionScheme, animation duration, easing | references/material3-motion.md |

| PR URL, code review, "review this PR", "what's wrong with this" | references/pr-review.md |

| Session start, project detection | references/auto-init.md |

| Atomic design, design system, reusable component, component library, design tokens | references/atomic-design.md |

4. Apply and verify

• Write code that follows the patterns in the reference
• Flag any anti-patterns you see in the user's existing code
• Suggest the minimal correct solution — don't over-engineer

4a. Component building mode

When the request involves building a component (composable that renders UI):

• Consult references/atomic-design.md
• Classify the component level (atom, molecule, organism, template)
• Apply the "Ask" prompt from Section 5 before scaffolding code
• Ensure the component satisfies the atom contract (modifier, slots, tokens, defaults)

5. Cite the source

When referencing Compose internals, point to the exact source file:

// See: compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/Composer.kt

Key Principles

• Compose thinks in three phases: Composition → Layout → Drawing. State reads in each

phase only trigger work for that phase and later ones.

• Recomposition is frequent and cheap — but only if you help the compiler skip unchanged

scopes. Use stable types, avoid allocations in composable bodies.

• Modifier order matters. Modifier.padding(16.dp).background(Color.Red) is visually

different from Modifier.background(Color.Red).padding(16.dp).

• State should live as low as possible and be hoisted only as high as needed. Don't put

everything in a ViewModel just because you can.

• Side effects exist to bridge Compose's declarative world with imperative APIs. Use the

right one for the job — misusing them causes bugs that are hard to trace.

• Compose Multiplatform shares the runtime but not the platform. UI code in

commonMain is portable. Platform-specific APIs (LocalContext, BackHandler,

Window) require expect/actual or conditional source sets.

Source Code Receipts

Beyond the guidance docs, this skill bundles the actual source code from

androidx/androidx (branch: androidx-main) and JetBrains/compose-multiplatform-core

(branch: jb-main). When you need to verify how something works internally, or the

user asks "show me the actual implementation", read the raw source from

references/source-code/:

| Module | Source Reference | Key Files Inside |

|--------|-----------------|------------------|

| Runtime | references/source-code/runtime-source.md | Composer.kt, Recomposer.kt, State.kt, Effects.kt, CompositionLocal.kt, Remember.kt, SlotTable.kt, Snapshot.kt |

| UI | references/source-code/ui-source.md | AndroidCompositionLocals.android.kt, Modifier.kt, Layout.kt, LayoutNode.kt, ModifierNodeElement.kt, DrawModifier.kt |

| Foundation | references/source-code/foundation-source.md | LazyList.kt, LazyGrid.kt, BasicTextField.kt, Clickable.kt, Scrollable.kt, Pager.kt |

| Material3 | references/source-code/material3-source.md | MaterialTheme.kt, ColorScheme.kt, Button.kt, Scaffold.kt, TextField.kt, NavigationBar.kt |

| Navigation | references/source-code/navigation-source.md | NavHost.kt, ComposeNavigator.kt, NavGraphBuilder.kt, DialogNavigator.kt |

| CMP | references/source-code/cmp-source.md | Window.kt, ComposeUIViewController.kt, UIKitView.kt, ComposeViewport.kt, ResourceReader.kt |

Two-layer approach

• Start with guidance — read the topic-specific reference (e.g., references/state-management.md)
• Go deeper with source — if the user wants receipts or you need to verify, read from references/source-code/

Source tree map

androidx/androidx (branch: androidx-main)
├── compose/runtime/runtime/src/commonMain/kotlin/androidx/compose/runtime/
├── compose/ui/ui/src/androidMain/kotlin/androidx/compose/ui/platform/
├── compose/ui/ui/src/commonMain/kotlin/androidx/compose/ui/
├── compose/foundation/foundation/src/commonMain/kotlin/androidx/compose/foundation/
├── compose/material3/material3/src/commonMain/kotlin/androidx/compose/material3/
├── compose/navigation/navigation-compose/src/commonMain/kotlin/androidx/navigation/compose/
├── tv/tv-material/src/main/java/androidx/tv/material3/
└── tv/tv-foundation/src/main/java/androidx/tv/foundation/

compose-multiplatform-core (branch: jb-main)
├── compose/ui/ui/src/desktopMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/iosMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/webMain/kotlin/androidx/compose/ui/window/
├── compose/ui/ui/src/skikoMain/kotlin/androidx/compose/ui/
└── compose/foundation/foundation/src/skikoMain/kotlin/androidx/compose/foundation/

compose-multiplatform (resources library)
└── components/resources/library/src/commonMain/