Using Strong Skipping Correctly — make every restartable composable skippable, intentionally

Strong Skipping Mode is the Compose compiler behavior that became the default with the Kotlin Compose compiler plugin shipped in Kotlin 2.0.20. It changes two things at once: every restartable composable becomes skippable regardless of param stability (unstable params are compared with ===, stable params with equals), and every capturing lambda literal written inside a @Composable function is automatically wrapped in remember(captures) { ... }. Both behaviors are on by default; neither requires opt-in flags on Kotlin 2.0.20+. Lambdas with no captures are already compiler-emitted singletons and are NOT wrapped — only capturing lambdas need (and get) the auto-remember treatment.

That sounds like "stability no longer matters", and for a lot of UI code it almost is. But the change leaves three sharp edges: stable types still need correct equals semantics so the === fallback does not invalidate every recompose, lambdas in non-@Composable scopes (LazyListScope.items { }, Modifier.pointerInput { }, plain object expressions) are not auto-memoized, and a few intentional cases need explicit opt-out via @DontMemoize or @NonSkippableComposable. This skill walks the verification, audit, and escape-hatch decisions for working in a strong-skipping world.

When to use this skill

• The developer asks "do I still need @Stable?" or "does this composable skip now?".
• A composable still recomposes on every parent tick even though the developer "thought strong skipping fixed that".
• A lambda allocation question comes up — "is this onClick = { vm.add(it) } allocating per recompose?".
• Migrating a project from Kotlin 1.9.x / Compose Compiler 1.5.x to Kotlin 2.0.20+ and reconciling reports that now show restartable skippable everywhere.
• The developer encounters @DontMemoize or @NonSkippableComposable in code or compiler output and asks what they do.
• The user mentions "strong skipping", "auto-remember", "@DontMemoize", "@NonSkippableComposable", or "skippable everywhere".

When NOT to use this skill

• The conceptual question is "what makes a type stable in the first place?" — use ../../stability/understanding-stability-inference/SKILL.md.
• Stability is regressing silently and the team needs a CI gate — use ../../stability/enforcing-stability-in-ci/SKILL.md.
• Even with strong skipping on, type-level stability still matters for diagnostic clarity and for equals-based skipping to work — use ../../stability/diagnosing-compose-stability/SKILL.md to fix the underlying types.
• The recomposition is happening but the developer cannot see it — use ../debugging-recompositions/SKILL.md to instrument first.

Prerequisites

• Kotlin 2.0.20+ with the Compose compiler Gradle plugin applied via org.jetbrains.kotlin.plugin.compose. Strong Skipping is on by default. To turn it off on Kotlin 2.0.20+, use composeCompiler { featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled()) } (the legacy enableStrongSkippingMode = true property is @Deprecated("Use the featureFlags option instead") and still works on older Kotlin).
• Compose Compiler reports turned on for the module under audit (see ../../stability/diagnosing-compose-stability/SKILL.md).
• Builds running in release when reading reports — debug adds Live Literals which distort skip behavior (see ../../measurement/testing-compose-in-release-mode/SKILL.md).
• Familiarity with the per-composable line format in *-composables.txt (restartable skippable fun Foo(...)).

Workflow

1. Verify strong skipping is actually active

Before claiming any behavior is "because of strong skipping", confirm the toolchain is on a version where it is the default, or the legacy flag is set.

./gradlew :app:dependencies --configuration kotlinCompilerPluginClasspathRelease | grep -i compose

Expect the Compose compiler plugin to come from Kotlin 2.0.20 or later. In build.gradle.kts:

plugins {
    alias(libs.plugins.kotlin.android)        // Kotlin 2.0.20+
    alias(libs.plugins.kotlin.compose)        // org.jetbrains.kotlin.plugin.compose
}

To disable strong skipping on Kotlin 2.0.20+ (the modern feature-flag DSL):

import androidx.compose.compiler.plugins.kotlin.ComposeFeatureFlag

composeCompiler {
    featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled())
}

The legacy property composeCompiler { enableStrongSkippingMode = true } is @Deprecated("Use the featureFlags option instead") in modern Compose Compiler Gradle plugin releases. It still works (and is still the only switch on older Kotlin 1.9.x / 2.0.0–2.0.10), but new code should prefer featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled()) when opting out.

Then regenerate Compose Compiler reports and grep for a known previously-unstable signature:

./gradlew :app:assembleRelease
grep -A1 "restartable" app/build/compose_compiler/app-release-composables.txt | head -40

Under strong skipping, every restartable composable should print restartable skippable, including ones that take List<Foo> or other unstable parameters. If a composable is still listed restartable without skippable, it is using @NonSkippableComposable (intentional) or the mode has been turned off (e.g. someone added featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled()) or set the legacy enableStrongSkippingMode = false).

2. Audit lambda capture sites inside @Composable scopes

Strong skipping wraps every capturing lambda literal written inside a @Composable function in remember(captures) { ... }. The captured-values list is the compiler-generated remember key. Capture-less lambdas (e.g. { vm.refresh() } where vm is a stable file-scope reference, or { /* no-op */ }) are already compiler-emitted singletons and are NOT auto-remembered — there is nothing to key on. Three consequences:

• A capture-less lambda is a single shared instance across all recompositions of the surrounding function (singleton emitted by the compiler).
• A lambda that captures only stable values is memoized once via remember(captures) and re-used across recompositions while the captures compare equal.
• A lambda that captures an unstable value (e.g. a List<Foo> literal not hoisted) re-captures on every recompose because the unstable capture compares with ===, and a fresh literal is a new reference.

Inspect the suspect call site. The mental model: "what does this lambda close over, and is each capture stable by equals and identity-stable across recompositions?".

// RIGHT — captures stable id + stable callback; auto-remembered by strong skipping
@Composable
fun Row(snack: Snack, onClick: (Long) -> Unit) {
    Button(onClick = { onClick(snack.id) }) { Text(snack.name) }
}

// WRONG — captures a freshly allocated list literal; new reference each recompose
@Composable
fun Header(title: String) {
    Toolbar(actions = listOf(Action.Share, Action.Save)) { /* ... */ }
}
// WRONG because: `listOf(...)` allocates a new List every recompose. Even with strong
// skipping the unstable param compares with ===, fails, and Toolbar recomposes every time.

// RIGHT — hoist the unstable literal so its identity is stable
@Composable
fun Header(title: String) {
    val actions = remember { listOf(Action.Share, Action.Save) }
    Toolbar(actions = actions) { /* ... */ }
}

3. Identify the gaps where strong skipping does NOT memoize

Auto-remember only applies to lambdas inside a `@Composable` function context. The following are not @Composable scopes; lambdas inside them are not auto-remembered and need a manual remember(key) if allocation matters:

• LazyListScope.items { ... }, LazyGridScope.items { ... }, LazyVerticalGrid.items { ... }, etc. — the items block is a regular Kotlin DSL builder.
• Modifier.pointerInput { ... }, Modifier.draggable { ... }, Modifier.scrollable { ... } — non-@Composable lambdas.
• Object expressions and SAM conversions (e.g. object : DefaultLifecycleObserver { }).
• Modifier.drawBehind { ... }, Modifier.drawWithCache { ... } — the lambda parameters are not @Composable.
• Coroutine builders inside non-@Composable scopes.

For these, hoist a stable lambda yourself, keyed on whatever may change:

// WRONG — onClick allocated per item per recompose; strong skipping does not reach here
LazyColumn {
    items(snacks, key = { it.id }) { snack ->
        SnackRow(snack, onClick = { vm.select(snack.id) })
    }
}
// WRONG because: `items { snack -> ... }` is LazyListScope, not a @Composable function.
// Strong skipping does not auto-remember the onClick lambda — a new instance allocates per row,
// per recompose, and SnackRow's `===` comparison on the lambda param fails every time.

// RIGHT — hoist a stable handler keyed on the stable callback
LazyColumn {
    items(snacks, key = { it.id }) { snack ->
        val onClick = remember(snack.id) { { vm.select(snack.id) } }
        SnackRow(snack, onClick = onClick)
    }
}

// RIGHT — even better: pass the id-aware callback once
LazyColumn {
    items(snacks, key = { it.id }) { snack ->
        SnackRow(snack, onClick = vm::select)   // method reference is stable
    }
}

4. Decide on escape hatches

Strong skipping is opinionated. A handful of cases legitimately need the opposite behavior. The full reference table is in references/escape-hatches.md; the high-level decision tree:

• `@DontMemoize` at a lambda expression site (the annotation targets EXPRESSION only, not TYPE) — the lambda must NOT be auto-remembered. Use when the lambda intentionally captures a fresh value per call (e.g. a logger that should record the latest counter, not the one captured by the first composition). Apply it at the call site: Button(onClick = @DontMemoize { ... }), never at a parameter type position like (@DontMemoize () -> Unit).
• `@NonSkippableComposable` on a function — opt the function out of skipping entirely. Use for side-effect-only composables (a logger, a debug overlay) that must run on every recompose regardless of param equality.
• `@NonRestartableComposable` on a function — drop the restart scope entirely. Use only for very small composables where the restart bookkeeping costs more than the function body. Almost never needed in app code; Compose UI uses it internally.
• `@ReadOnlyComposable` on a function — declare the function only reads composition values and produces no nodes, so it can run in initialization contexts (e.g. computing a value to pass into another composable). Compose's MaterialTheme.colorScheme getters use it.

// RIGHT — logger composable that must always emit
@NonSkippableComposable
@Composable
fun RecompositionLogger(label: String) {
    SideEffect { Log.d("Recomp", "tick: $label @ ${System.currentTimeMillis()}") }
}

// RIGHT — annotate the lambda expression that intentionally captures fresh per-call state.
// @DontMemoize is @Target(EXPRESSION) — apply it on the lambda literal, NOT on the type.
@Composable
fun TraceClicks(counter: Int, content: @Composable (() -> Unit) -> Unit) {
    content(@DontMemoize { Log.d("Click", "counter at click time = $counter") })
}

5. Prove behavior with @TraceRecomposition

Reading reports tells the story up to the function boundary. To confirm a specific composable is or is not being skipped at runtime, instrument with @TraceRecomposition from compose-stability-analyzer. Cross-link ../../measurement/tracing-recompositions-at-runtime/SKILL.md for the full setup. The two-line summary:

@TraceRecomposition(traceStates = true)
@Composable
fun SnackRow(snack: Snack, onClick: (Long) -> Unit) { /* ... */ }

Logcat will print one line per recomposition with the changed parameters, which directly answers "did strong skipping skip this call or not?".

Patterns

Pattern: stability still matters even under strong skipping

Strong skipping does not eliminate the need for @Immutable / @Stable. It changes the comparison from equals to === for unstable params. === is reference equality. If a stable type is needed in a hot path, mark it @Immutable so equals is used and structurally-equal instances skip.

// WRONG
data class Filter(val tags: List<String>, val sort: SortOrder)

@Composable
fun FilterBar(filter: Filter) { /* ... */ }
// WRONG because: Filter is unstable (List<String> is unstable). Strong skipping makes
// FilterBar skippable, but only when `prevFilter === newFilter`. A copy() with the same
// content fails identity, recomposes the bar, every time.

// RIGHT
@Immutable
data class Filter(val tags: ImmutableList<String>, val sort: SortOrder)

@Composable
fun FilterBar(filter: Filter) { /* ... */ }
// RIGHT because: @Immutable + ImmutableList makes Filter stable. Strong skipping uses
// equals(), and structurally-equal copies skip.

Pattern: literal collection in a hot composable param

// WRONG
@Composable
fun Toolbar(title: String) {
    ActionRow(actions = listOf(Action.Share, Action.Save))
}
// WRONG because: a fresh List allocates per recompose. Strong skipping makes ActionRow
// skippable, but the List param fails === every time and the body re-runs.

// RIGHT
private val ToolbarActions = persistentListOf(Action.Share, Action.Save)

@Composable
fun Toolbar(title: String) {
    ActionRow(actions = ToolbarActions)
}

Pattern: lambda inside LazyListScope.items

See workflow step 3. The short version: items { } is not @Composable, strong skipping does not reach inside it, hoist a stable callback or use a method reference.

Pattern: @DontMemoize for intentionally-fresh lambdas

// WRONG — auto-remembered lambda captures `counter` from the FIRST composition
@Composable
fun LoggingButton(counter: Int) {
    Button(onClick = { Log.d("Btn", "counter = $counter") }) { Text("hit") }
}
// WRONG because: under strong skipping the lambda is auto-remembered, but `counter` is a
// stable Int capture, so the remember key is the int value. This is actually fine here.
// Where it bites is when the developer EXPECTS each invocation to capture fresh state but
// the lambda is being passed across a memoization boundary that hides the capture.

// RIGHT — explicit opt-out where freshness is the contract.
// @DontMemoize is @Target(EXPRESSION) — apply on the lambda literal, never on the type.
@Composable
fun TraceContent(latest: Int, body: @Composable (() -> Unit) -> Unit) {
    body(@DontMemoize { sendTelemetry("snapshot=$latest") })
}

@DontMemoize is rarely needed in app code. Reach for it only after measuring; the default behavior is correct for almost all UI.

Pattern: @NonSkippableComposable for side-effect-only composables

// RIGHT
@NonSkippableComposable
@Composable
fun FrameTicker(onTick: () -> Unit) {
    SideEffect { onTick() }
}

The annotation says "this composable has work to do every recomposition; do not let the skip guard short-circuit it". Use sparingly — most composables that "must run every time" are actually misplaced state reads; fix the read site first.

Pattern: pair with CI to prevent strong-skipping regressions

Strong skipping makes nearly every composable skippable in the report, which makes the report less useful for spotting regressions by eye. Combine with ../../stability/enforcing-stability-in-ci/SKILL.md so the baseline diff catches a composable that flips from skippable to not.

Mandatory rules

• MUST verify the Kotlin / Compose compiler plugin version before claiming strong skipping is active. Print ./gradlew :app:dependencies and confirm Kotlin 2.0.20+ (default ON). On older Kotlin, confirm the legacy enableStrongSkippingMode = true flag in composeCompiler { }. If the project explicitly disables Strong Skipping via featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled()), treat the rest of this skill as not applicable.
• MUST NOT declare a composable "skippable now thanks to strong skipping" without checking the actual *-composables.txt report. Annotations like @NonSkippableComposable and lambdas inside LazyListScope.items { } remain footguns the report makes visible.
• MUST prefer @Immutable / @Stable over relying on reference equality for unstable types passed in hot paths. === is a poor substitute for structural equals when the producer of the value (copy(), map { }, builder DSL) does not preserve identity.
• MUST NOT use @DontMemoize or @NonSkippableComposable without a one-line code comment explaining why. These are advanced opt-outs; the next reader will assume they are mistakes if the rationale is not co-located.
• MUST NOT treat strong skipping as a substitute for hoisting unstable literals. A listOf(...) allocated in a composable param fails === regardless of strong skipping. Hoist into remember { ... } or a top-level persistentListOf(...).
• PREFERRED: combine this skill with ../../stability/enforcing-stability-in-ci/SKILL.md so a composable regressing from skippable to not skippable (e.g. someone adds @NonSkippableComposable without justification) fails CI.
• PREFERRED: when a developer asks "is my lambda allocated per recompose?", confirm the call site is inside a @Composable function before answering yes/no. The answer flips entirely at the @Composable boundary.

Skippability is a diagnostic, not a KPI: under strong skipping every composable is "skippable" in the report, but only the ones whose params actually compare equal will skip at runtime. The interesting question is no longer "is it skippable?" but "do its params compare equal across the recomposition the developer cares about?".

Verification

• [ ] Confirmed Kotlin / Compose compiler version is 2.0.20+ (default ON) and that no featureFlags.add(ComposeFeatureFlag.StrongSkipping.disabled()) opt-out is in effect — or, on older Kotlin, that the legacy enableStrongSkippingMode = true flag is set.
• [ ] *-composables.txt shows restartable skippable on previously-unstable-param composables.
• [ ] Audited the suspect call site for unstable literal captures (listOf, mapOf, ad-hoc lambdas in non-@Composable scopes).
• [ ] Any @DontMemoize / @NonSkippableComposable / @NonRestartableComposable / @ReadOnlyComposable in the changed code has a co-located comment explaining why.
• [ ] Runtime confirmed via @TraceRecomposition (see ../../measurement/tracing-recompositions-at-runtime/SKILL.md) that the composable skips when its inputs are equal.
• [ ] Stability baseline (see ../../stability/enforcing-stability-in-ci/SKILL.md) covers the changed module so a future regression in skip behavior fails CI.

References

• Strong Skipping (Android Developers) — https://developer.android.com/develop/ui/compose/performance/stability/strongskipping
• Ben Trengrove, "Jetpack Compose Strong Skipping Mode explained" — https://medium.com/androiddevelopers/jetpack-compose-strong-skipping-mode-explained-cbdb2aa4b900
• Ben Trengrove, "New ways of optimizing stability in Jetpack Compose" — https://medium.com/androiddevelopers/new-ways-of-optimizing-stability-in-jetpack-compose-038106c283cc
• Compose Compiler release notes — https://developer.android.com/jetpack/androidx/releases/compose-compiler
• Compose stability overview — https://developer.android.com/develop/ui/compose/performance/stability
• Chris Banes, "Composable metrics" — https://chrisbanes.me/posts/composable-metrics/
• skydoves, "Optimize App Performance by Mastering Stability" — https://medium.com/proandroiddev/optimize-app-performance-by-mastering-stability-in-jetpack-compose-69f40a8c785d
• skydoves/compose-stability-analyzer — https://github.com/skydoves/compose-stability-analyzer
• references/escape-hatches.md — full reference table of @NonRestartableComposable, @NonSkippableComposable, @DontMemoize, @ReadOnlyComposable with code samples and decision matrix.

For diagnosing why a composable is unstable in the first place, see ../../stability/diagnosing-compose-stability/SKILL.md. For instrumenting a specific composable to see if it actually skips at runtime, see ../debugging-recompositions/SKILL.md and ../../measurement/tracing-recompositions-at-runtime/SKILL.md. For preventing a strong-skipping regression in CI, see ../../stability/enforcing-stability-in-ci/SKILL.md.