juanjosegongi/12-principles-of-animation

12 Principles of Animation

Review animation code for compliance with Disney's 12 principles adapted for web interfaces.

How It Works

1. Read the specified files (or prompt user for files/pattern)
2. Check against all rules below
3. Output findings in file:line format

Rule Categories

| Priority | Category | Prefix | |----------|----------|--------| | 1 | Timing | timing- | | 2 | Easing | easing- | | 3 | Physics | physics- | | 4 | Staging | staging- |

Rules

Timing Rules

timing-under-300ms

User-initiated animations must complete within 300ms.

Fail:

.button { transition: transform 400ms; }

Pass:

.button { transition: transform 200ms; }

timing-consistent

Similar elements must use identical timing values.

Fail:

.button-primary { transition: 200ms; }
.button-secondary { transition: 150ms; }

Pass:

.button-primary { transition: 200ms; }
.button-secondary { transition: 200ms; }

timing-no-entrance-context-menu

Context menus should not animate on entrance (exit only).

Fail:

<motion.div initial={{ opacity: 0 }} animate={{ opacity: 1 }} />

Pass:

<motion.div exit={{ opacity: 0 }} />

Easing Rules

easing-entrance-ease-out

Entrances must use ease-out (arrive fast, settle gently).

Fail:

.modal-enter { animation-timing-function: ease-in; }

Pass:

.modal-enter { animation-timing-function: ease-out; }

easing-exit-ease-in

Exits must use ease-in (build momentum before departure).

Fail:

.modal-exit { animation-timing-function: ease-out; }

Pass:

.modal-exit { animation-timing-function: ease-in; }

easing-no-linear-motion

Linear easing should only be used for progress indicators, not motion.

Fail:

.card { transition: transform 200ms linear; }

Pass:

.progress-bar { transition: width 100ms linear; }

easing-natural-decay

Use exponential ramps, not linear, for natural decay.

Fail:

gain.gain.linearRampToValueAtTime(0, t + 0.05);

Pass:

gain.gain.exponentialRampToValueAtTime(0.001, t + 0.05);

Physics Rules

physics-active-state

Interactive elements must have active/pressed state with scale transform.

Fail:

.button:hover { background: var(--gray-3); }
/* Missing :active state */

Pass:

.button:active { transform: scale(0.98); }

physics-subtle-deformation

Squash/stretch deformation must be subtle (0.95-1.05 range).

Fail:

<motion.div whileTap={{ scale: 0.8 }} />

Pass:

<motion.div whileTap={{ scale: 0.98 }} />

physics-spring-for-overshoot

Use springs (not easing) when overshoot-and-settle is needed.

Fail:

<motion.div transition={{ duration: 0.3, ease: "easeOut" }} />
// When element should bounce/settle

Pass:

<motion.div transition={{ type: "spring", stiffness: 500, damping: 30 }} />

physics-no-excessive-stagger

Stagger delays must not exceed 50ms per item.

Fail:

transition={{ staggerChildren: 0.15 }}

Pass:

transition={{ staggerChildren: 0.03 }}

Staging Rules

staging-one-focal-point

Only one element should animate prominently at a time.

Fail:

// Multiple elements with competing entrance animations
<motion.div animate={{ scale: 1.1 }} />
<motion.div animate={{ scale: 1.1 }} />

staging-dim-background

Modal/dialog backgrounds should dim to direct focus.

Fail:

.overlay { background: transparent; }

Pass:

.overlay { background: var(--black-a6); }

staging-z-index-hierarchy

Animated elements must respect z-index layering.

Fail:

.tooltip { /* No z-index, may render behind other elements */ }

Pass:

.tooltip { z-index: 50; }

Output Format

When reviewing files, output findings as:

file:line - [rule-id] description of issue

Example:
components/modal/index.tsx:45 - [timing-under-300ms] Exit animation 400ms exceeds 300ms limit
components/button/styles.module.css:12 - [physics-active-state] Missing :active transform

Summary Table

After findings, output a summary:

| Rule | Count | Severity | |------|-------|----------| | timing-under-300ms | 2 | HIGH | | physics-active-state | 3 | MEDIUM | | easing-entrance-ease-out | 1 | MEDIUM |

References

• The Illusion of Life: Disney Animation
• Apple WWDC23: Animate with Springs