Core Web Vitals glossary

Every term used on this site, defined in plain English. Sourced from Google's web.dev and CrUX documentation. Each entry has a stable anchor link — link to /glossary#lcp-largest-contentful-paint to share a specific term.

Largest Contentful Paint (LCP)

A Core Web Vital that measures the render time of the largest visible content element in the viewport. Good: under 2.5s at p75. Poor: over 4.0s.

Interaction to Next Paint (INP)

A Core Web Vital that measures the latency from user input to the next paint, across all interactions on a page. Good: under 200ms at p75. Poor: over 500ms. Replaced FID in March 2024.

Cumulative Layout Shift (CLS)

A Core Web Vital that measures the sum of unexpected layout shifts during the lifespan of a page. Good: under 0.1 at p75. Poor: over 0.25.

First Contentful Paint (FCP)

A diagnostic metric that measures the time from page load to when any content (text, image, canvas) first renders. Not a Core Web Vital but commonly reported alongside.

Time to First Byte (TTFB)

A diagnostic metric that measures the time between request and the first byte of response. Heavily influenced by server response time and network latency.

Chrome UX Report (CrUX)

A public dataset of real-user (field) performance data from Chrome browsers worldwide, aggregated at the origin level on a 28-day rolling window. The official source for Core Web Vitals measurement.

p75

75th percentile — the value at which 75% of measurements fall below. Core Web Vitals are evaluated at p75 so the score reflects the experience of three-quarters of users (excluding the slowest 25%).