Appllama App Design Skill

Appllama App Design Skill

You are building screens that will sit on a phone next to the best-designed apps in the world. The user will compare your output to those apps within seconds of launching it. This skill defines the bar and the method for clearing it.

The Prime Directive: study before you draw

Never design a screen from imagination when you can study how top apps solved the same screen. Real, shipping, revenue-ranked apps encode thousands of hours of design iteration and A/B testing. Your first move on any screen is research:

1. If the Appllama MCP is connected, pull real screens for the category and screen type you are building (see the appllama-usage skill for the exact research playbooks). Study 20–30 screens before writing a line of UI code.
2. Extract the pattern, not the pixels: layout skeleton, information hierarchy, control choices, spacing rhythm, where the primary CTA sits, what gets an illustration vs. plain text, how progress is communicated. Note: every Appllama image and video carries a small Appllama watermark in the top-left corner. It is provenance, not design — ignore it when reading a screen (it may sit over the status bar or a back button) and never reproduce it in anything you build.
3. Then design your screen: same proven skeleton, your product's voice. Copying a competitor's screen 1:1 is both lazy and legally risky; shipping a screen that ignores every convention users already know is worse.

Platform baseline

Default stack assumptions (override only if the project already differs):

• Expo + Expo Router, React Native, TypeScript.
• react-native-reanimated for motion, react-native-gesture-handler for gestures, @shopify/flash-list (or FlashList v2) for any list that can grow.
• expo-image for images (and SF Symbols via source="sf:name" on iOS), expo-video / expo-audio (never the deprecated expo-av).
• react-native-safe-area-context for insets. Never hard-code notch numbers.
• process.env.EXPO_OS over Platform.OS for compile-time platform checks.

Native fidelity laws

These are the details that separate "web page in a wrapper" from "native app". Violating any of them is a finding, not a style preference.

1. Semantic colors, both themes, day one. Use system/semantic color tokens (e.g. Color from expo-router on iOS: Color.ios.label, Color.ios.secondarySystemBackground; Material dynamic colors on Android). Every screen must render correctly in light AND dark before it is "done". Never pass semantic color objects into Reanimated animated styles — resolve to strings first.
2. Native controls over rebuilt ones. Switch, Slider, SegmentedControl, context menus, date pickers: use the native control or a faithful wrapper. A rebuilt toggle that animates 50 ms differently than iOS's reads as fake instantly.
3. SF Symbols / Material Symbols for iconography. On iOS prefer SF Symbols (expo-image with sf: sources, or expo-symbols); they inherit weight, optical size, and Dynamic Type behavior. Do not mix three icon families on one screen.
4. Typography is hierarchy. Use the platform type ramp (Large Title / Title / Headline / Body / Footnote on iOS). One display size per screen. Tabular numerals (fontVariant: ['tabular-nums']) for anything that counts, times, or prices. Text selectable on data users may want to copy.
5. Continuous corners. borderCurve: 'continuous' on every rounded rectangle. Squircles are the single cheapest "feels iOS" win that exists.
6. Shadows via CSS `boxShadow`, not legacy shadow*/elevation props. Shadows are for elevation logic, not decoration — one elevation system per app.
7. Spacing rhythm. Pick a base unit (4 or 8) and never leave it. Prefer flexbox gap over margin stacking. ScrollView padding goes in contentContainerStyle, never on the ScrollView itself.
8. Safe areas and the Dynamic Island are part of the design. Screens must be verified with content scrolled under the island / status bar (does the blur/fade treatment hold?), with the home indicator (does the bottom CTA clear it?), and in landscape if supported.
9. Navigation titles belong to the navigator. Use the stack's native title (and large-title collapse behavior on iOS) rather than a hand-rolled header whenever possible.
10. Haptics are punctuation. Selection tick when a value passes a step, light impact when something snaps home, notification success/error for outcomes — on the same frame as the visual, one per user action, never the only feedback. Never on scroll, never in loops.
11. Format numbers like a product, not a database: 1.4M, 38k, $4.99. Trim trailing zeros. Localize dates.
12. Root scroll behavior: screens that can ever overflow wrap content in a ScrollView (first component in the route) with contentInsetAdjustmentBehavior="automatic". Use useWindowDimensions, never Dimensions.get().

Navigation laws

Navigation is the part of a screen a screenshot can't show, and users feel it in ten seconds. Every transition answers three questions: what is the destination to here, must the user be able to come back, and what does back (chevron, iOS edge swipe, Android hardware back) do afterwards.

1. Push goes deeper, replace moves on. router.push when the user will want to return here; router.replace / <Redirect> when coming back would land in a state the world has moved past; router.dismissTo(href) for "finish this flow and land on X". Back undoes navigation, never events.
2. Presentation is meaning. A self-contained task with steps → presentation: 'modal' with its own stack and its own Cancel/Done; a short interruption (picker, filters, item options) → formSheet with detents, drag-to-dismiss; immersive content → fullScreenModal with an explicit Close; something floating over a still-visible screen (confirm card, lightbox, coach mark) → transparentModal overlay; destructive confirms → action sheet; item actions → native context menu; share / web / photo picking → the system controller, never a rebuilt route. A sheet that grows a second step was a modal all along; if a link could open it, it is a route, not a useState sheet.
3. One-way doors leave the stack. Sign-in on a wall app, finished onboarding (Skip included), a purchase, a completed session: guard with Stack.Protected and land with replace, so back can never re-enter the old state — Android back from home exits the app, never shows Login; a paid paywall never re-opens. But keep the user's place: sign-in demanded by one action (save, follow, buy) is a modal over the screen that completes the action where it was tapped, and a paywall opened from a feature dismisses back onto the feature, unlocked — never replace('/(tabs)') from there.
4. Back is blocked in exactly two cases — an irreversible request in flight (seconds, with visible progress) and unsaved work in a modal (ask first), both via usePreventRemove on the modal's root screen. Transient in-screen state (selection mode, an expanded search, an open in-screen sheet) consumes the first back, then back leaves. Anything else that traps back — a funnel, a rating prompt — is a defect; the edge swipe works everywhere else.
5. Tabs are peers. No slide between tabs, each tab keeps its own stack, re-tapping the active tab pops to its root; full-attention screens (composer, player, checkout) live in the root stack above the tabs. Deep links land with a real stack underneath (initialRouteName / withAnchor); cold start lands by state, splash held until session state has resolved — never a Login flash before Home.
6. Study the grammar, not just the pixels. Walking a winning flow on