INP (Interaction to Next Paint) is a new metric added to Google's Core Web Vitals in March 2024, replacing the old FID. INP measures how quickly the site responds when the user interacts (click, tap, keyboard). The metric directly affects UX and Google factors it into ranking.
Why INP replaces FID
FID was used from 2018 and measured only the first interaction. That isn't enough β users interact many times, and later interactions may be slow.
INP measures all interactions during the page's lifetime and uses the worst (about the 75th percentile). This shows Google the real UX level.
INP values
Google's thresholds: Good β under 200ms. Needs Improvement β 200-500ms. Poor β over 500ms β noticeable slowness, ranking penalty.
Main INP factors
First β JavaScript execution time. If a function runs 200ms+, INP is poor. Main causes: large JS files, heavy computation, many DOM updates.
Second β render blocking. If the main thread is busy, the browser can't respond. Long Tasks (50ms+) are the main enemy of INP.
Third β third-party JS. Analytics, Pixel, chat β all add JS. More means worse INP.
Improvement strategies
1. JS optimisation: code splitting, tree shaking, dynamic import.
2. Break long tasks. A function 50ms+ β split via setTimeout, requestIdleCallback, scheduler.yield.
3. Web Workers β move heavy computation to a separate thread. The main thread stays free for interaction.
Managing third-party
Only necessary third-party tags. Defer/async so they don't block.
Better β server-side integration. GA4 via GTM Server Container, Facebook Conversions API. More complex but effective.
Measuring INP
Real values come from the Chrome User Experience Report (CrUX) β in GSC's \"Core Web Vitals\". Lab tests (Lighthouse, PageSpeed) are simulated.
Chrome DevTools Performance panel β for debugging.
INP and SPAs
In SPAs INP is usually worse β client-side routing and dynamics increase JS work. React, Vue β page transitions involve large JS work.
Optimisation: React Server Components, Vue Streaming. Hard but reduces JS load.
Sayt.uz INP
Sayt.uz INP is 120ms, in the green zone. This is the result of PHP returning full HTML with minimal JS. 95% of interactions are under 150ms.
This signals Google and gives a ranking boost for passing Core Web Vitals.