INP
Quick Definition
INP (Interaction to Next Paint) is a Core Web Vitals metric that measures page responsiveness by tracking the delay between a user interaction and the next visual update. A good INP score is 200 milliseconds or less.
Why It Matters
INP replaced FID (First Input Delay) as a Core Web Vitals metric in March 2024. It measures how responsive your page is to all user interactions throughout their visit, not just the first click. A slow INP means buttons feel laggy and forms feel unresponsive, frustrating users and hurting your rankings.
Real-World Example
You click 'Add to Cart' on a shopping site but nothing happens for 500 milliseconds. Then you click again, accidentally adding two items. That delayed response is what INP measures. A good INP score means every click, tap, and keyboard input gets a visual response within 200 milliseconds.
Signal Connection
Trust -- A responsive page feels trustworthy and professional. When users click a button and see an immediate response, they trust that the site is working correctly. Slow interactions create doubt and frustration, eroding user trust.
Pro Tip
The biggest INP killers are heavy JavaScript execution and long tasks on the main thread. Use Chrome DevTools Performance panel to identify 'Long Tasks' (anything over 50ms). Break these into smaller chunks using requestIdleCallback or Web Workers.
Common Mistake
Confusing INP with page load speed. INP does not measure how fast your page loads initially -- that is LCP. INP measures how quickly the page responds to user interactions after it has loaded. A page can load fast but still have poor INP if JavaScript blocks the main thread during interactions.
Test Your Knowledge
What does INP (Interaction to Next Paint) measure?
Show Answer
Answer: B. How quickly the page responds to user interactions like clicks and taps
INP measures the delay between a user interaction (click, tap, key press) and the next visual update on screen. A good INP is 200ms or less. It replaced FID as a Core Web Vitals metric because it measures all interactions, not just the first one.