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 (native stack, formSheet routes, NativeTabs), React Native, TypeScript.
• react-native-reanimated 4 + react-native-worklets for motion, react-native-gesture-handler for gestures, expo-haptics, react-native-keyboard-controller for anything that tracks the keyboard, @shopify/flash-list (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.
• Install with npx expo install <pkg> so versions match the SDK; never hand-roll a component a listed package already solves (references/native-controls.md has the picks).

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. selectionAsync when a value ticks past a step, light impact when something snaps home or a drag commits, notification success/error for outcomes. Same frame as the visual, one per user action, never the only feedback — and never on scroll, never per frame, never on an entrance the user didn't cause.

Navigation laws

Navigation is the part of a screen you can't screenshot, and users feel it within ten seconds. Every transition answers three questions: what is the destination to here (deeper → push; a self-contained task → modal; a short interruption → form sheet; must see through → overlay; a replacement of where I am → replace), must the user be able to come back, and what does back do afterwards — chevron, edge swipe, Android hardware back, active-tab re-tap. The full method, verb by verb and case by case, is references/navigation.md. The laws:

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. Don't rely on navigate to unwind — dismissTo(href) says "finish and land on X".
2. Presentation is meaning. A self-contained task with steps is a modal with its own stack and its own Cancel/Done; a short interruption is a formSheet with detents; immersive content is a fullScreenModal with an explicit Close; something that must sit on top of a visible screen is a transparentModal overlay; destructive confirms are action sheets; item actions are context menus; tasks the OS already owns — share, open a web page, pick a photo, compose mail, rate the app — are system controllers, never routes. A sheet that grows a second step was a modal all along. If a link could open it, it is a route.
3. One-way doors remove themselves from history. Sign-in / sign-up on a wall app, onboarding completion (Skip included), a purchase, a finished session, an expired target: Stack.Protected guards and 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 closes and completes the action there — never a replace('/(tabs)') — and a paywall opened from a feature dismisses back onto the feature, unlocked, not to a tab root.
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 through usePreventRemove, never to keep someone in a funnel. One more case consumes back without blocking it: transient in-screen state — selection/edit mode, an expanded search field, an open in-screen sheet — clears on the first back and the next back leaves the screen (BackHandler in useFocusEffect, returning true only while that state is up; usePreventRemove when iOS should hold too). A BackHandler that returns true to keep someone on a screen is a defect. Everywhere else the iOS edge swipe and Android hardware back work, always.
5. Bottom tabs are peers. No slide in the tab bar (a Material-styled app may cross-fade; swipe-paged top tabs inside a screen are a pager, not this), each tab keeps its stack, re-tapping the active tab pops to root (and, at the root, scrolls to top); full-attention screens (composer, player, checkout) live in the root stack the tabs so the tab bar gets out of the way.

Anti-slop laws

AI-built apps share a look, and users file it under "template" within seconds. Each of these is a default ban — there is always an override when the brand explicitly asks for the thing AND you can articulate why it fits this product.

1. No AI-default styling. Purple/indigo gradient CTAs with a glow, glassmorphism on every card, mesh-gradient heroes, confetti for minor events, sparkles in headings — that is the model's house style, not design. Your palette, materials, and layout come from the reference screens you studied, never from the priors you'd reach for unprompted.
2. One accent, locked. Pick one accent color and it is THE accent on every screen — no blue CTA on one screen and teal on the next, no new hue appearing in screen seven. Neutrals carry the app; the accent is spent where the money is (primary action, active state, progress).
3. One grey family. Warm greys or cool greys — never both in one app.
4. Shape lock. One corner-radius scale, stated as a rule ("actions are pills, cards 16, inputs 8") and never violated. Mixed radii without a stated rule read as assembled-from-parts.
5. No emoji as iconography. Icons are SF Symbols / Material Symbols (fidelity law 3). Emoji appear only when the product's voice is genuinely chat-native or playful — sparingly, in content, never in chrome.
6. One label per intent. "Get started", "Start now", and "Begin" are the same intent — pick one phrasing and use it everywhere it appears.
7. Emphasis stays in the family. Emphasize a word with weight or italic of the same typeface; injecting a serif word into a sans headline (or vice versa) for visual interest is amateur.
8. Ship full state cycles, not the happy path. Static-successful-state- only is the default failure mode: skeletons must match the final layout's shape, empty states are composed (and say how to fill them), errors are inline and specific.
9. The slop pre-flight is mechanical. Before any flow reaches the simulator pass, count: distinct accent hues (must be 1), distinct corner radii (all from the stated scale), emoji in UI chrome (0), gradients without a brand reason (0), duplicate labels for one intent (0). A failed count is a fix, not a judgment call.

Motion laws

Motion is the highest-leverage polish surface and the easiest to overdo. Decisions are made in order — the method, the exact values and the implementation are in references/motion.md; the physics of feel in references/fluid-interfaces.md.

• The frequency gate comes first. Something met 100+ times a day (tab switch, keyboard, scroll, back) gets nothing beyond the platform default; tens a day gets near-imperceptible (<150 ms); occasional (sheets, modals, toasts) gets standard motion; the delight budget is spent only on rare, first-time moments. The tab bar never slides (swipe-paged top tabs are a pager the finger drives — a different thing). Screen transitions stay at the platform default (a native-stack animation value like fade for an overlay is the platform; a JS-rebuilt transition or a changed duration is not). Passing this gate with zero lines of code is a success.
• Name the purpose in one word — feedback, spatial consistency, state indication, preventing a jarring change, explanation, delight — or don't build it. Data the user is reading never moves for style.
• Cheapest tool that works: a Reanimated CSS transition for state changes, layout animations for mount/unmount/reflow, shared values + gestures only for what a finger touches or scroll drives, the native stack for screens, formSheet for sheets, NativeTabs for tabs, native menus for menus. transform and opacity only (an absolute, childless element may animate width); never scale(0).
• If a finger was involved, it's a spring — from the live value, with the release velocity handed in, interruptible at any instant, rubber-banded at boundaries, committed by momentum (a flick is enough). One spring vocabulary per app: SETTLE { duration: 400, dampingRatio: 1 }, SNAP { 400, 0.8 }, SHEET { 300, 0.8 }; bounce only after momentum.
• Everything else is timing, under 300 ms, strong ease-out — Easing.bezier(0.23, 1, 0.32, 1) to enter/exit, (0.77, 0, 0.175, 1) to move on screen; never ease-in on an entrance or an on-screen change (a Material-styled app's exits may use M3's accelerate curve — motion.md §5). Press feedback 100–150 ms, on press-in, matched to the element class — scale 0.97 for buttons/cards/tiles, a background highlight (never scale) for list rows and cells, opacity for bar buttons and plain-text actions. Exits faster than entrances, along the same path.
• Off the JS thread. No setState in a gesture or scroll handler, no scheduleOnRN/runOnJS per frame, no shared-value reads in render, no PanResponder, no entering on recycled list rows, no animated height to collapse a header, no JS-rebuilt screen transition.

State architecture

Screens that feel great are screens whose state is boring:

• Server state in TanStack Query (or the project's equivalent): caching, retries, optimistic updates. Never useEffect+fetch.
• Client state in a small atomic store (Zustand/Jotai). Broad "app state" contexts cause the re-render cascades that make UIs feel heavy.
• Ephemeral UI state (open/closed, focus, scroll) stays local to the component.
• Optimistic by default: taps reflect instantly, reconcile in the background, roll back loudly on failure.
• Uncontrolled TextInputs for high-frequency typing surfaces; controlled inputs are a top-3 cause of typing jank.
• Persist tiny client state in MMKV, not AsyncStorage, when latency shows.

Perceived performance

• Skeletons only for content whose shape you know; otherwise progressive reveal. Never a full-screen spinner for a partial update.
• FlashList for every list that can grow; give stable keys.
• Preload the next screen on press-in (router.prefetch / <Link prefetch> plus its data), not on navigation-complete.
• Images: right-size sources, expo-image with recyclingKey in lists, thumbhash/blurhash placeholders.
• Cold-start TTI and bundle discipline live in references/performance.md — apply the measure → optimize → re-measure loop, never blind memoization.

Image & illustration assets

When a screen calls for illustration, empty-state art, hero imagery, or icons beyond the symbol set:

• Generate assets with the best image model available to you (e.g. an imagegen tool or the Higgsfield MCP/CLI if connected) at the highest quality settings, then downscale to @1x/@2x/@3x. Never upscale.
• One visual language per app: pick a style (gradient-mesh, flat-duotone, 3D-clay, hand-drawn, mascot style) and generate ALL assets in that same style, same palette, same lighting. A mixed-style asset set reads as template slop.
• Prompt for transparent or solid-flat backgrounds matched to your surface color; composite artifacts (white halos, wrong-color mattes) are an automatic redo.
• Full asset pipeline and prompt patterns: references/image-assets.md.

The simulator loop (non-negotiable)

A screen does not exist until you have seen it running. The loop:

1. Implement → launch in the iOS Simulator (or Android emulator).
2. Screenshot and actually look: alignment, optical centering, spacing rhythm, truncation with long content, dark mode, Dynamic Type at XL.
3. Run the full-motion pass below — screenshots prove layout; they prove nothing about motion.
4. Fix, relaunch, re-verify. Repeat until you cannot find a defect — then run the checklist in references/simulator-loop.md once more.

Do not declare a screen finished from code review alone. Do not stop at "looks fine" — stop at "cannot find a flaw at 100% zoom".

The full-motion pass (mandatory, per flow)

Every flow is evaluated as moving pictures in the simulator, never as stills. Screen-record the entire flow end to end (xcrun simctl io booted recordVideo flow.mov), exercising ALL of it:

• every screen transition, push/pop, tab switch
• every modal and sheet: present, drag, dismiss — and cancel mid-drag
• every back path: chevron, edge swipe, Android hardware back, active-tab re-tap — and, after each one-way door (sign-in, onboarding done, purchase, finished session), an attempt to go back that must fail to re-enter the old state
• the keyboard, both directions: appear (does the layout glide, is the focused input visible?) and dismiss (does anything jump-cut?)
• every user interaction: press states, gesture follow-through, interrupted gestures, rapid taps, scroll flings at the extremes

Watch the recording twice: once at full speed for feel, once scrubbing frame by frame. You are hunting:

• dropped or stuttered frames — the bar is a sustained 60 fps through every transition, measured, not vibed
• one-frame flashes: white/unstyled first paint, wrong-theme frames mid- transition, color pops where a surface briefly renders the wrong token
• layout jumps, double-render pops, springs that clip or overshoot into content, elements that reflow after appearing

The whole recording must play like one native piece — smooth end to end, zero UX glitches. One glitchy frame means the flow is not done.

Definition of done, per screen

• Studied 20–30 real reference screens for this screen type (the Prime Directive's bar; 10+ only when the Appllama MCP is unavailable or the library is thin for the category — say so) and can name the pattern you adopted
• Navigation answered: what this screen is (push / modal / sheet / overlay / replace), what back does from it on iOS and Android, and — if it sits behind a one-way door — that back cannot re-enter the old state; modals carry Cancel/Done; deep links land with a stack
• Light + dark mode verified in the simulator
• Safe areas / Dynamic Island / home indicator verified
• Long-content, empty, loading, and error states designed — not defaulted
• Motion passed the gate (frequency tier + named purpose for every animation; nothing slides between bottom tabs; screen transitions native), uses the app's one spring/easing vocabulary, runs off the JS thread, and every gesture hands its velocity to a spring
• Motion: the full flow screen-recorded and scrubbed — entrances, presses, transitions, modals, keyboard — native feel, zero glitch or wrong-color frames; Reduce Motion respected; 60 fps measured on a release build on the slowest supported device
• Dynamic Type XL doesn't break layout; text is selectable where useful
• All tap targets ≥ 44pt; contrast passes in both themes
• Assets: single style family, crisp at @3x, no compositing halos
• List surfaces virtualized; no controlled-input jank; no re-render storms (profiled, not guessed)

References