# Designesy — /spring-validator Canonical page: https://www.designesy.org/spring-validator --- ## Spring Physics Validator Spring-based motion is the frontier — M3 Expressive, iOS, Framer Motion, React Spring. But no one validates whether a spring's physics produce overshoot that violates reduced-motion requirements. Until now. Input stiffness, damping, and mass. Get the damping ratio, overshoot percentage, settle time, and an accessibility verdict: does this spring require explicit reduced-motion suppression? Preset springs Accessibility verdict ✓ Safe — no reduced-motion concern Damping ratio ζ = 0.990 produces no perceptible overshoot. This spring is safe for vestibular sensitivity without explicit reduced-motion suppression. Damping ratio (ζ) 0.990 underdamped Overshoot 0.0% visible Settle time (2%) 286ms to equilibrium Rise time 111ms to equilibrium Natural freq 2.25 Hz 14.1 rad/s Damped freq 0.32 Hz 2.0 rad/s Spring response — displacement over time Reduced-motion compliance checklist Spring does not produce perceptible overshoot (>2%) If overshoot > 2%, the spring is visible to vestibular-sensitive users Underdamped springs have explicit @media (prefers-reduced-motion: reduce) rule Underdamped springs MUST be suppressed or replaced under reduced-motion Settle time ≤ 300ms (UI animation bound) UI animation should stay at or below 300ms unless justified Overshoot ≤ 10% (not a vestibular trigger) Overshoot > 10% is clearly visible and likely triggers discomfort Spring uses transform/opacity only (no layout animation) Never animate width, height, margin, padding — use transform and opacity CSS snippet — with reduced-motion fallback ``` .spring-underdamped { /* Damping ratio: ζ = 0.990 · Overshoot: 0.0% */ transition: transform 286ms cubic-bezier(0.2, 0, 0, 1); } @media (prefers-reduced-motion: reduce) { .spring-underdamped { /* Suppress overshoot — linear or ease-out at 150ms */ transition: transform 150ms ease-out; } } ``` ## Why this exists Material Design 3 Expressive introduced spring-based motion backed by 46 research studies. But M3 has *no published reduced-motion token* for springs. The spec describes spring physics (damping, response) but does not address what happens when a user has`prefers-reduced-motion: reduce`set and a spring with a low damping ratio produces visible overshoot. This is a green-field validation capability. The Designesy contract already ships spring tokens (`damping: 1.0, response: 0.4` for default, `damping: 0.8, response: 0.3` for momentum). This tool lets anyone verify whether their spring parameters are safe for vestibular sensitivity — or whether they need an explicit reduced-motion fallback. The physics: a spring's damping ratio (ζ) determines its behavior. ζ > 1 is overdamped (no overshoot, slow). ζ = 1 is critically damped (no overshoot, fastest settle). 0 < ζ < 1 is underdamped (overshoots, oscillates). The lower the damping ratio, the more visible the overshoot — and the more likely it triggers vestibular discomfort in sensitive users.