Website Performance Optimization & Reporting Flashcards

Which Core Web Vitals metric replaced First Input Delay (FID) in March 2024?

Answer: Interaction to Next Paint

Interaction to Next Paint (INP) replaced FID as the responsiveness Core Web Vital because it measures all interactions, not just the first.

A page's LCP is 3.4 seconds at the 75th percentile of field data. How does Google classify it?

Answer: Needs improvement

LCP of 2.5s or less is good, 2.5-4.0s needs improvement, and over 4.0s is poor.

Which CLS score is considered 'good' for Core Web Vitals?

Answer: 0.1 or less

A Cumulative Layout Shift of 0.1 or less at the 75th percentile is rated good.

Why is field data often preferred over lab data for judging real user experience?

Answer: It reflects real devices, networks, and user behavior

Field (RUM) data captures the variety of real devices and connections, whereas lab data is a controlled simulation.

Which technique most directly reduces Largest Contentful Paint for a hero image?

Answer: Preloading the hero image and using a modern format

Preloading the LCP resource and serving compressed formats like WebP/AVIF speeds up its render.

A tag manager container grows to include 40 third-party tags and page speed drops. What is the best analytics-aware response?

Answer: Audit tags, remove unused ones, and fire non-critical tags later

Auditing and deferring non-essential tags retains needed measurement while cutting main-thread cost.

What does Time to First Byte (TTFB) primarily indicate?

Answer: Server and network responsiveness to the initial request

TTFB measures how long the browser waits for the first byte of the response, reflecting server and network latency.