INP (Interaction to Next Paint)
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DEFINITION
The Core Web Vitals responsiveness metric. Measures the 75th-percentile latency of all user interactions on a page (click, tap, key) from input to the next paint. Replaced FID in March 2024. Goal: under 200ms at p75. Killers: long main-thread tasks, oversized event handlers, hydration battles, non-yielding React renders. Track via PerformanceObserver on `event` entries or the web-vitals lib in RUM; lab tools (Lighthouse) only approximate.
- SSR (Server-Side Rendering)→
HTML rendered by the server per-request, fresh for every user. Ideal for dynamic content (dashboards), but slower than SSG.
- SSG (Static Site Generation)→
Pages are produced at build time as HTML and served from a CDN. Near-zero TTFB. DField's own site runs this way across 111+ pages.
- ISR (Incremental Static Regeneration)→
SSG + timed regeneration: the HTML is static but regenerates on a schedule. Ideal for blog content · freshness with CDN speed.
- Edge rendering→
Code runs at the CDN edge closest to the user (Cloudflare Workers, Vercel Edge). Dynamic responses with ~10–50 ms TTFB.
- RSC (React Server Components)→
React components that run exclusively on the server and never ship to the browser. Result: less client-side JS and faster hydration.
- LCP (Largest Contentful Paint)→
Time until the largest visible element paints. Google Core Web Vitals passes under 2.5s · we usually land marketing pages under 1s.
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