GSAP SvelteKit

mount → initial state → intro → settled → outro → end state → unmount

Mount and unmount belong to Svelte; animation owns the five phases between them. SvelteKit reuses pages on parameter changes and preserves shared layouts, so a new page lifecycle need not mean a new node.

Keep the requested look and existing project conventions. Add GSAP/plugins only as needed; do not replace the chosen animation library unless asked.

This skill decides when motion runs. For what moves, and for a feel such as premium or playful, also load the animaxxing skill when it is installed: its recipes and its guide to finding the vibe plug into this lifecycle.

Start with the project

Read repository instructions, existing animation, layouts, navigation, CSS, accessibility conventions, and checks. Then:

1. Confirm SvelteKit with Svelte 5 in runes mode. Plain Svelte without SvelteKit routing belongs to gsap-frameworks. For Svelte 4 or legacy mode, say so and map $effect advice onto onMount and onDestroy.
2. Read the installed @sveltejs/kit and svelte versions. Prefer their bundled types over memory: node_modules/@sveltejs/kit/types/index.d.ts documents every navigation object, and node_modules/svelte/types/index.d.ts the runes and lifecycle exports. Version gates: onNavigate (1.24), $app/state (2.12; use $app/stores before), to.scroll on navigation targets (2.51), prefersReducedMotion in svelte/motion (5.7), {@attach} (5.29).
3. Check svelte.config.js, page options (ssr, csr, prerender), data-sveltekit-preload-data on body in src/app.html, and links marked data-sveltekit-reload. A page with csr = false has no client router and no navigation hooks; a reload link is a full document load. Treat both as plain documents.

Choose the engine

Use Svelte transition: / in: / out: for simple block motion and {#key} swaps that only need DOM retention through an outro. Use View Transitions from onNavigate for snapshot morphs or page crossfades. Use GSAP for live-DOM navigation holds, interruptible sequences, split text, or scroll-linked motion. One engine per element; see combining engines.

Read only what you need

• Invisible entrances, failed initialization, indexing, and first-load performance: Initialization and recovery, plus the framework integration.
• Navigation hooks and their order, outro before navigation, the lock, back and forward, scroll, focus, links, preloading, View Transitions: SvelteKit navigation.
• Page reuse versus remount, layouts, {#key} versus afterNavigate, the Svelte 5 lifecycle, Svelte transitions beside GSAP, shallow-routed modals, SSR: Page lifetime.
• The five phases, GSAP setup, contexts, show and hide, layout stability, scroll, text, plugins: Lifecycle implementation.
• Lenis, ScrollSmoother, or eased page scrolling across routes: Smooth scrolling, plus the hook mapping.
• Curtains, first-visit preloaders, and shared-element morphs: Transition archetypes, plus the layout integration.
• Touch, viewport changes, and device budgets: Devices and input.
• Tauri, Electron, or Wails desktop shells: Desktop webviews.
• Before calling work done: Verification.

Install the official GSAP skills alongside this repository. Load gsap-core for API details and gsap-frameworks for component setup only as needed.

Rules

• Preserve invisible intros on successful setup; recover the current incoming owner on failure. Follow the initialization contract before adding hiding rules.
• GSAP runs only in the browser. onMount and $effect never run on the server; module-level code needs a browser guard. Scope selectors with gsap.context to a bind:this root. Clean up every tween, trigger, split, and listener in the effect teardown or the onMount return.
• Reserve final geometry with normal CSS and a stable wrapper; overlap outgoing/incoming content without doubling layout space.
• Mount, then set initial values, then paint. Successful initialization never flashes settled content before the intro. Server HTML paints before hydration, so hide intro targets only under a root attribute set by an inline script, only during the initial phase, with a no-JavaScript path.
• Clear temporary styles at settled. Use will-change only while animating; this overrides gsap-performance's static hint.
• Use capability queries for device tiers. Touch states release; controls work without hover.
• Keep outgoing pages mounted and visible through outro and end state. Hold the navigation with beforeNavigate and re-issue it from the end callback, or return the outro's promise from onNavigate. The URL changes before onNavigate runs, so only the first keeps it unchanged during the outro.
• A navigation to the same route with new params updates the page in place. Run the lifecycle again from afterNavigate against DOM that already holds settled values, or remount with {#key}.
• Back and forward arrive as popstate through the same hooks. Never run an outro for them. Give them an intro-only path after scroll restoration.
• Do not read page, data, or navigating inside the effect that builds GSAP setup unless it should rebuild on every navigation.
• One engine per element. An out: directive on a node GSAP also animates fights it, and the block stays in the DOM until the directive finishes.
• Keep native link behavior, data-sveltekit-* options, focus, scroll, and no-JavaScript readability.
• Reduced motion reaches the same settled state and still fires every completion callback. Svelte transitions ignore CSS reduced-motion rules; zero them from prefersReducedMotion.
• Define interruption and rapid-click behavior; completion must release navigation waits exactly once.
• Verify in a real browser when practical. Use a production build for route, config, dependency, or release changes.