Web Vitals is an initiative by Google to provide unified guidance for
quality signals that are essential to delivering a great user experience on the
web.
Google has provided a number of tools over the years to measure and
report on performance. Some developers are experts at using these tools, while
others have found the abundance of both tools and metrics challenging to keep
up with.
Site owners should not have to be performance experts to understand the
quality of experience they are delivering to their users. The Web Vitals
initiative aims to simplify the landscape, and help sites focus on the metrics
that matter most, the Core Web Vitals.
Core Web
Vitals
Core Web Vitals are the subset of Web Vitals that apply to all web
pages, should be measured by all site owners, and will be surfaced across all
Google tools. Each of the Core Web Vitals represents a distinct facet of the
user experience, is measurable in the field, and reflects the real-world
experience of a critical user-centric outcome.
The metrics that make up Core Web Vitals will evolve over time. The current set for 2020 focuses on three aspects of the user experience—loading, interactivity, and visual stability—and includes the following metrics (and their respective thresholds):
Largest Contentful Paint
(LCP): measures loading performance. To
provide a good user experience, LCP should occur within 2.5 seconds of
when the page first starts loading.
First Input Delay (FID):
measures interactivity. To provide a good user experience, pages
should have a FID of 100 milliseconds or less.
Cumulative Layout Shift
(CLS): measures visual stability. To provide a
good user experience, pages should maintain a CLS of 0.1. or
less.
For each of the above metrics, to ensure you're hitting the recommended
target for most of your users, a good threshold to measure is the 75th
percentile of page loads, segmented across mobile and desktop devices.
Tools that assess Core Web Vitals compliance should consider a page
passing if it meets the recommended targets at the 75th percentile for all of
the above three metrics.
