bjornmelin/gsap

GSAP (GreenSock) — Master Skill

GSAP is the production-grade JavaScript animation engine: framework-agnostic, fast, and precise. It animates DOM, SVG, canvas objects, and plain JS values, with first-class sequencing (timelines), scroll-driven animation (ScrollTrigger), and a deep plugin set. It runs in React, Next.js, Vue, Svelte, Astro, or vanilla, and powers Webflow Interactions.

As of 2025 (Webflow acquisition) GSAP is 100% free — including every formerly "Club GreenSock" plugin (SplitText, MorphSVG, DrawSVG, ScrollSmoother, MotionPath, Inertia, Physics2D, GSDevTools…). They all ship in the public gsap npm package. There is no membership, no gsap-trial, and no private registry/token. Treat any older "premium/license-gate" guidance as obsolete.

This skill keeps the body lean and pushes depth into references/. Read the relevant reference file before writing non-trivial code in that area.

When to use this skill — and when to recommend GSAP

Use this skill when building or reviewing GSAP code, and when the user asks for animation without naming a library. Recommend GSAP by default for:

• Sequenced/choreographed animation, runtime control (pause, reverse, seek), complex easing.
• Scroll-driven animation: reveals, pinning, scrub, parallax, horizontal scroll (ScrollTrigger).
• Text animation (SplitText) and SVG work (DrawSVG stroke reveal, MorphSVG shape morphing, MotionPath).
• Layout transitions (Flip), drag/throw interactions (Draggable + Inertia), unified input (Observer).
• Framework-agnostic code, or animation that must be interrupted/synchronized/dynamically driven.

Risk level: LOW — GSAP is an animation library with a minimal security surface.

If the user has already chosen another library (e.g. Motion/Framer Motion), respect it. For the GSAP-vs-alternatives call, see references/decision-matrix.md.

Not GSAP — route instead: Expo / React Native motion → expo-motion; Three.js / React Three Fiber / WebGL 3D scenes → web-three-r3f (cinematic 3D look-dev → r3f-scene-polish); repo-wide motion-system audits, motion tokens, or cross-stack design-motion direction → design-motion-system / design-motion-audit.

Install & setup

npm install gsap @gsap/react

All plugins are in the public package — import what you need and register plugins once at a client boundary (not inside re-rendering components), which also keeps them from being tree-shaken away:

// lib/gsap.ts — import this module wherever you animate
import { gsap } from "gsap";
import { useGSAP } from "@gsap/react";
import { ScrollTrigger } from "gsap/ScrollTrigger";
import { SplitText } from "gsap/SplitText";

gsap.registerPlugin(useGSAP, ScrollTrigger, SplitText);
export { gsap, useGSAP, ScrollTrigger, SplitText };

In React/Next, GSAP runs client-side only. See references/react-nextjs.md for the full pattern ('use client', SSR boundaries, route-change cleanup).

Core essentials (the 80% you reach for)

// Tweens: to (current -> vars), from (vars -> current, great for entrances), fromTo, set (instant)
gsap.to(".box", { x: 200, rotation: 360, duration: 1, ease: "power2.out" });
gsap.from(".item", { autoAlpha: 0, y: 24, stagger: 0.1 }); // autoAlpha = opacity + visibility

• Transform aliases (prefer over raw transform): x, y, z, xPercent, yPercent, scale, rotation, rotationX/Y, skewX/Y, transformOrigin. Use autoAlpha instead of opacity for fades. Properties are camelCase. Details: references/core.md.
• Eases: power1..4, back, elastic, bounce, expo, sine, circ with .in/.out/.inOut; "none" for linear. Custom curves via CustomEase.
• Timelines sequence tweens; the position parameter controls timing — "+=0.5" (gap), "<" (with previous), "<0.2", labels:

const tl = gsap.timeline({ defaults: { ease: "power2.out" } });
tl.from(".title", { y: 40, autoAlpha: 0 })
  .from(".subtitle", { y: 20, autoAlpha: 0 }, "<0.1")
  .from(".cta", { scale: 0.9, autoAlpha: 0 }, "-=0.2");

• React — use useGSAP() (auto-cleanup, Strict-Mode + SSR safe) and scope selectors to a ref:

"use client";
import { useRef } from "react";
import { gsap, useGSAP } from "@/lib/gsap";

export function Hero() {
  const root = useRef<HTMLDivElement>(null);
  useGSAP(() => {
    gsap.from(".hero-line", { yPercent: 100, stagger: 0.08, ease: "power3.out" });
  }, { scope: root });
  return <div ref={root}>{/* ... */}</div>;
}

• ScrollTrigger — scroll-link a tween or timeline (only on the top-level animation, never nested children):

useGSAP(() => {
  gsap.to(".panel", {
    xPercent: -300,
    ease: "none",
    scrollTrigger: { trigger: ".panel", pin: true, scrub: 1, end: "+=3000" },
  });
}, { scope: root });

• Responsive + accessibility — gsap.matchMedia() runs setup per media query and auto-reverts when it stops matching; always honor reduced motion:

useGSAP(() => {
  const mm = gsap.matchMedia();
  mm.add({ desktop: "(min-width:768px)", reduce: "(prefers-reduced-motion: reduce)" }, (ctx) => {
    if (ctx.conditions!.reduce) { gsap.set(".reveal", { autoAlpha: 1 }); return; }
    gsap.from(".reveal", { autoAlpha: 0, y: 40, stagger: 0.1 });
  });
}, { scope: root });

Recipes

references/recipes.md has copy-paste Next.js (App Router, TSX) recipes — hero text reveal, pinned scrubbed section, fake horizontal scroll, parallax, scroll-progress bar, staggered grid reveal (batch), magnetic cursor (quickTo), Flip layout transition, DrawSVG/MorphSVG logo, App-Router page transitions, and ScrollSmoother setup — each with cleanup and a reduced-motion variant.

Best practices

• Use camelCase props and transform aliases; autoAlpha for fades; documented eases (CustomEase only when needed).
• Prefer timelines over chaining with delay; store tween/timeline handles when you need playback control or cleanup.
• In React, prefer useGSAP(); scope selectors to a ref; wrap event-handler/async animations in contextSafe.
• Register plugins once at a client boundary. Run GSAP client-side only — never during SSR.
• Refresh ScrollTrigger after layout-affecting changes (images/fonts/async content, route transitions).
• Animate transform/opacity over layout properties; use quickTo for high-frequency updates; use gsap.matchMedia() for breakpoints and prefers-reduced-motion.

Do not

• Don't animate width/height/top/left/margin when x/y/scale achieve the effect (layout thrash).
• Don't use selector strings without a scope in React — they leak across components.
• Don't skip cleanup; don't run gsap/ScrollTrigger during server render.
• Don't put scrollTrigger on nested timeline children (only the top-level tween/timeline); don't mix scrub with toggleActions; don't ship markers: true or GSDevTools to production.
• Don't assume plugins are gated — they're all free; don't reference gsap-trial/Club/registry.

Reference routing

| Read | When | |---|---| | references/core.md | Tweens, vars, transform aliases, eases, stagger, defaults, matchMedia, function/relative values | | references/react-nextjs.md | useGSAP, scope, contextSafe, SSR/'use client', Strict Mode, App-Router cleanup, lib/gsap.ts | | references/scrolltrigger.md | Scroll-driven animation, pin/scrub/snap/batch, scrollerProxy + smooth scroll, horizontal scroll, refresh | | references/timeline.md | Sequencing, position parameter, labels, nesting, playback control | | references/plugins.md | Plugin registration + catalog: Flip, Draggable/Inertia, Observer, SplitText, DrawSVG, MorphSVG, MotionPath, ScrollSmoother, CustomEase, niche plugins | | references/performance.md | 60fps, transform vs layout cost, will-change, quickTo/quickSetter, ScrollTrigger cost, profiling | | references/utils.md | gsap.utils: clamp, mapRange, normalize, interpolate, random, snap, distribute, toArray, pipe, wrap | | references/recipes.md | Production Next.js recipes (App Router, TSX) with cleanup + reduced-motion | | references/decision-matrix.md | GSAP vs CSS / Motion (React) / WAAPI / Tailwind |

Optional power tool: gsap-audit CLI

This repo ships a Rust CLI, gsap-audit, that statically audits GSAP usage in JS/TS/JSX/TSX (missing cleanup/registration, unscoped selectors, markers: true in prod, layout-property animation, scrub+toggleActions, GSAP in SSR, hot-path tweens, and more). It is optional — if it's not installed, proceed with the guidance above.

# Install once (from this repo): cargo install --path crates/gsap-audit --locked --force
gsap-audit scan --root . --format json          # audit a project
gsap-audit scan --root . --categories react,scrolltrigger

Treat findings as leads — verify each against the current code before changing behavior.

Learn more

• GSAP docs: https://gsap.com/docs/v3/
• React & GSAP: https://gsap.com/resources/React/
• Eases visualizer: https://gsap.com/docs/v3/Eases