For a long time, "fast" meant "loads quickly". That still matters, but the web has shifted its attention to what happens after the page appears: how quickly it responds when you tap, how smoothly it moves between views, and whether animation helps or gets in the way.
Responsiveness is now a Core Web Vital
In March 2024, Interaction to Next Paint (INP) replaced First Input Delay as a Core Web Vital. Where the old metric looked only at the first interaction, INP considers the responsiveness of interactions throughout a visit. Slow INP usually comes down to long tasks on the main thread — heavy JavaScript, large re-renders, work that could have waited.
- Break up long tasks, and yield to the browser between chunks of work.
- Do less on interaction: update what changed, defer what can wait.
- Keep third-party scripts on a short leash, and measure with real-user data, not only lab tests.
Smooth navigation without a framework's help
The View Transitions API lets browsers animate between states and, increasingly, between whole pages, with a few lines of CSS. What once needed a single-page app and custom animation code can now be progressive enhancement: supporting browsers get the transition, others simply navigate.
Motion that runs off the main thread
Scroll-linked effects built with JavaScript scroll listeners tend to lag behind the scroll and compete with everything else on the main thread — which is what makes them feel janky. CSS scroll-driven animations tie motion directly to scroll position and let the browser run it on the compositor, so it stays in step. Animating only transform and opacity keeps it cheap.
Motion with manners
Motion should explain — where something came from, what changed, what to look at — rather than decorate. Keep it brief and consistent, and always honour the prefers-reduced-motion setting: for some people, movement isn't a delight but a trigger.
Our Web Design & Development team builds for real-world responsiveness, and our Motion & Animation practice designs movement that is purposeful and performant.