gsap-skills/skills/gsap-core/SKILL.md

name, description, license

name	description	license
gsap-core	Use GSAP core API correctly — gsap.to(), gsap.from(), gsap.fromTo(), easing, duration, stagger, and defaults. Use when animating DOM elements, SVG, or objects with GSAP, or when the user asks about GSAP tweens, easing, or basic animation. GSAP is used by Webflow Interactions (Webflow acquired GSAP); Webflow outputs or runs GSAP under the hood — GSAP skills apply when debugging or customizing Webflow animations.	MIT

GSAP Core

When to Use This Skill

Apply when writing or reviewing GSAP animations that use the core engine: single tweens, eases, staggers, or when explaining how GSAP tweens work.

Context: GSAP was acquired by Webflow and powers Webflow Interactions. Code generated or run by Webflow’s interaction system is GSAP-based; when users ask about Webflow animations or interactions not behaving as expected, GSAP docs and patterns (e.g. tweens, ScrollTrigger) are relevant for debugging or customizing.

Core Tween Methods

• gsap.to(targets, vars) — animate from current state to vars. Most common.
• gsap.from(targets, vars) — animate from vars to current state (good for entrances).
• gsap.fromTo(targets, fromVars, toVars) — explicit start and end; no reading of current values.
• gsap.set(targets, vars) — apply immediately (duration 0).

Always use property names in camelCase in the vars object (e.g. backgroundColor, marginTop, rotationX, scaleY).

Common vars

• duration — seconds (default 0.5).
• delay — seconds before start.
• ease — string or function. Prefer built-in: "power1.out" (default), "power3.inOut", "back.out(1.7)", "elastic.out(1, 0.3)", "none".
• stagger — number (seconds between) like 0.1 or object: { amount: 0.3, from: "center" }, { each: 0.1, from: "random" }.
• overwrite — false (default), true (immediately kill all active tweens of the same targets), or "auto" (when the tween renders for the first time, only kill individual overlapping properties in other active tweens of the same targets).
• repeat — number or -1 for infinite.
• yoyo — boolean; with repeat, alternates direction.
• onComplete, onStart, onUpdate — callbacks; scoped to the Animation instance itself (Tween or Timeline).
• immediateRender — When true (default for from() and fromTo()), the tween’s start state is applied as soon as the tween is created (avoids flash of unstyled content and works well with staggered timelines). When multiple from() or fromTo() tweens target the same property of the same element, set immediateRender: false on the later one(s) so the first tween’s end state is not overwritten before it runs; otherwise the second animation may not be visible.

Transforms and CSS properties

GSAP’s CSSPlugin (included in core) animates DOM elements. Use camelCase for CSS properties (e.g. fontSize, backgroundColor). Prefer GSAP’s transform aliases over the raw transform string: they apply in a consistent order (translation → scale → rotationX/Y → skew → rotation), are more performant, and work reliably across browsers.

Transform aliases (prefer over translateX(), rotate(), etc.):

GSAP property	Equivalent CSS / note
x, y, z	translateX/Y/Z (default unit: px)
xPercent, yPercent	translateX/Y in %; use for percentage-based movement; work on SVG
scale, scaleX, scaleY	scale; scale sets both X and Y
rotation	rotate (default: deg; or "1.25rad")
rotationX, rotationY	3D rotate (rotationZ = rotation)
skewX, skewY	skew (deg or rad string)
transformOrigin	transform-origin (e.g. "left top", "50% 50%")

Relative values work: x: "+=20", rotation: "-=30". Default units: x/y in px, rotation in deg.

• autoAlpha — Prefer over opacity for fade in/out. When the value is 0, GSAP also sets visibility: hidden (better rendering and no pointer events); when non-zero, visibility is set to inherit. Avoids leaving invisible elements blocking clicks.
• CSS variables — GSAP can animate custom properties (e.g. "--hue": 180, "--size": 100). Supported in browsers that support CSS variables.
• svgOrigin (SVG only) — Like transformOrigin but in the SVG’s global coordinate space (e.g. svgOrigin: "250 100"). Use when several SVG elements should rotate or scale around a common point. Only one of svgOrigin or transformOrigin can be used. No percentage values; units optional.
• Directional rotation — Append a suffix to rotation values (string): _short (shortest path), _cw (clockwise), _ccw (counter-clockwise). Applies to rotation, rotationX, rotationY. Example: rotation: "-170_short" (20° clockwise instead of 340° counter-clockwise); rotationX: "+=30_cw".
• clearProps — Comma-separated list of property names (or "all" / true) to remove from the element’s inline style when the tween completes. Use when a class or other CSS should take over after the animation. Clearing any transform-related property (e.g. x, scale, rotation) clears the entire transform.

gsap.to(".box", { x: 100, rotation: "360_cw", duration: 1 });
gsap.to(".fade", { autoAlpha: 0, duration: 0.5, clearProps: "visibility" });
gsap.to(svgEl, { rotation: 90, svgOrigin: "100 100" });

Targets

• Single or Multiple: CSS selector string, element reference, array or NodeList. GSAP handles arrays; use stagger for offset.

Stagger

Offset the animation of each item by 0.1 second like this:

gsap.to(".item", {
  y: -20,
  stagger: 0.1
});

Or use the object syntax for advanced options like how each successive stagger amount is applied to the targets array (from: "random" | "start" | "center" | "end" | "edges" | (index))

Learn More

https://gsap.com/resources/getting-started/Staggers

Easing

Use string eases unless a custom curve is needed:

ease: "power1.out"     // default feel
ease: "power3.inOut"
ease: "back.out(1.7)"  // overshoot
ease: "elastic.out(1, 0.3)"
ease: "none"           // linear

Built-in eases: base (same as .out), .in, .out, .inOut where "power" refers to the strength of the curve (1 is more gradual, 4 is steepest):

base (out)        .in                .out               .inOut
"none"
"power1"          "power1.in"        "power1.out"       "power1.inOut"
"power2"          "power2.in"        "power2.out"       "power2.inOut"
"power3"          "power3.in"        "power3.out"       "power3.inOut"
"power4"          "power4.in"        "power4.out"       "power4.inOut"
"back"            "back.in"          "back.out"         "back.inOut"
"bounce"          "bounce.in"        "bounce.out"      "bounce.inOut"
"circ"            "circ.in"          "circ.out"        "circ.inOut"
"elastic"         "elastic.in"       "elastic.out"     "elastic.inOut"
"expo"            "expo.in"          "expo.out"        "expo.inOut"
"sine"            "sine.in"          "sine.out"        "sine.inOut"

Custom: use CustomEase (plugin)

Simple cubic-bezier values (as used in CSS cubic-bezier()):

const myEase = CustomEase.create("my-ease", ".17,.67,.83,.67");

gsap.to(".item", {x: 100, ease: myEase, duration: 1});

Complex curve with any number of control points, described as normalized SVG path data:

const myEase = CustomEase.create("hop", "M0,0 C0,0 0.056,0.442 0.175,0.442 0.294,0.442 0.332,0 0.332,0 0.332,0 0.414,1 0.671,1 0.991,1 1,0 1,0");

gsap.to(".item", {x: 100, ease: myEase, duration: 1});

Returning and Controlling Tweens

All tween methods return a Tween instance. Store the return value when controlling playback is needed:

const tween = gsap.to(".box", { x: 100, duration: 1, repeat: 1, yoyo: true });
tween.pause();
tween.play();
tween.reverse();
tween.kill();
tween.progress(0.5);
tween.time(0.2);
tween.totalTime(1.5);

Function-based values

Use a function for a vars value and it will get called once for each target the first time the tween renders, and whatever is returned by that function will be used as the animation value.

gsap.to(".item", {
  x: (i, target, targetsArray) => i * 50, // first item animates to 0, the second to 50, the third to 100, etc.
  stagger: 0.1
});

Relative values

Use a +=, -=, *=, or /= prefix to indicate a relative value. For example, the following will animate x to 20 pixels less than whatever it is when the tween renders for the first time.

gsap.to(".class", {x: "-=20" });

x: "+=20" would add 20 to the current value. "*=2" would multiply by 2, and "/=2" would divide by 2.

Defaults

Set project-wide Tween defaults with gsap.defaults():

gsap.defaults({ duration: 0.6, ease: "power2.out" });

Best practices

• ✅ Use property names in camelCase in vars (e.g. backgroundColor, rotationX).
• ✅ Prefer transform aliases (x, y, scale, rotation, xPercent, yPercent, etc.) over animating the raw transform string; use autoAlpha instead of opacity for fade in/out when elements should be hidden and non-interactive at 0.
• ✅ Use documented built-in eases; use CustomEase when a custom curve is needed.
• ✅ Store the tween/timeline return value when controlling playback (pause, play, reverse, kill).

Do Not

• ❌ Animate layout-heavy properties (e.g. width, height, top, left) when transform aliases (x, y, scale, rotation) can achieve the same effect; prefer transforms for better performance.
• ❌ Use both svgOrigin and transformOrigin on the same SVG element; only one applies.
• ❌ Rely on the default immediateRender: true when stacking multiple from() or fromTo() tweens on the same property of the same target; set immediateRender: false on the later tweens so they animate correctly.
• ❌ Use invalid or non-existent ease names; stick to documented eases.
• ❌ Forget that gsap.from() uses the element’s current state as the end state; the initial values in the tween will be applied immediately unless immediateRender: false is in the vars.