H
ey folks. My name is Addy
Osmani and I manage the
Web Developer Insights
team in Chrome, where we work on
tools like PageSpeed Insights (https://
bit.ly/pagespeed-insights) and Lighthouse
(https://bit.ly/lighthouse-tool). Here, we’re
going to talk about the best thing since
sliced bread: performance measurement.
When you’re building a modern web
experience, it’s important to measure,
optimise and monitor if you’re to get
fast and stay fast. Performance plays
a significant role in the success of any
site, as high-performing sites engage
and retain users better than poorly-
performing ones. Tools like PageSpeed
Insights (PSI) and Lighthouse can be
valuable for monitoring the performance
of your sites. But what do they do?
Lighthouse offers a comprehensive
set of performance opportunities and
the time saved by implementing each
optimisation. You can find it in the
Chrome DevTools Audits panel and in
PageSpeed Insights.
PageSpeed Insights reports on the
performance of a page on mobile and
desktop devices and provides suggestions
on how that page may be improved.
PSI provides both ‘lab’ (Lighthouse)
and ‘field’ data about a page. Lab data
is useful for debugging performance
issues, as it is collected in a controlled
environment. However, it may not
capture real-world bottlenecks. Field data
is useful for capturing true, real-world
user experience but has a more limited
set of metrics.Performance score
At the top of the report, PSI provides
a score that summarises the page’s
performance. This score is determined
by running Lighthouse to collect and
analyse lab data about the page. A score
of 90 or above is considered fast and 50
to 90 is considered moderate. Below 50 is
considered to be slow.Lab versus field data
Lab data
Lab data is performance data collected
within a controlled environment with
predefined device and network settings.AUTHORADDY OSMANI
Osmani is an
engineering manager
working on Google
Chrome. He leads
teams working on
tools to help measure
site performance, like
Lighthouse, PageSpeed
Insights and efforts like
Headless Chrome.
w: https://addyosmani.com
t: @addyosmani
This offers reproducible results and
debugging capabilities to help identify,
isolate and fix performance issues.Strengths
O Helpful when it comes to debugging
any performance issues
O End-to-end and offers deep visibility
into the UX
O Provides reproducible testing and
debugging environmentLimitations
O Might not capture real-world
bottlenecks
O Cannot correlate against real-world
page KPIsNote: Tool s l i ke Lig ht house a nd
WebPageTest (https://www.webpagetest.
org/) collect this type of data.Field data
Field data (also called real user
monitoring, or RUM) is performance data
collected from real page loads your users
are experiencing in the wild.Strengths
O Captures true real-world user
experience
O Enables correlation to business key
performance indicatorsLimitations
O Restricted set of metrics
O Limited debugging capabilitiesNote: Public data sets like Chrome User
Experience Report (https://developers.
google.com/web/tools/chrome-user-
experience-report/) and performance
tools like the PageSpeed Insights speed
score report this type of data.Performance metrics
In the past, web performance has been
measured with the load event. However,
this moment doesn’t necessarily
correspond with what the user cares
about. Over the last few years, browser
teams have been working to standardise
a set of new metrics and APIs that more
accurately capture the performance of a
web page.Boost your PageSpeed Insights score