WebPageTest – The State of the Web

WebPageTest – The State of the Web


SPEAKER: As part of our
efforts to better understand the state of the
web, sometimes it’s helpful to take a step
back and look at the tools that enable us to understand how
individual websites are built. For example, as we explored
in an earlier episode, there are two things that make
the HTTP archives so powerful– its unique ability to
analyze the breadth of hundreds of
thousands of websites and the depth of information we
can learn about each website. And that’s where
WebPagetest comes in. It’s the engine that
drives the HTTP archive and tells us everything we
need to know about each page. Let’s see how it works. [MUSIC PLAYING] WebPagetest is a laboratory-like
environment where you have fine-grained controls over every
part of loading a web page– the device, browser, geographic
location, connection speed, cache state, and more. This kind of testing lends
itself really well to A/B testing. For example, you can test two
versions of the same web page with and without
some optimization to see exactly how it changes
the composition of the page. You could also test the same web
page over time and track things like how many bytes
it loads, a process known as synthetic monitoring. So let’s run our
first test by going to webpagetest.org and configure
a few common parameters. Running both a first
view and repeat view will show us the
difference a good caching policy makes on reload. Capturing video will
enable us to watch the visual progress of the page
load just as a user would see. For example, it could
show us the sequence of resources appearing on
the screen in slow motion or the flash of unstyled text
before the web fonts load. And now let’s enter the URL
of the page and run the test. When the results
are ready, it may be overwhelming to
try to take it all in, so let’s focus on the most
important thing first– the waterfall chart. This chart visualizes the
entire network activity of the page load. Each row represents a request
from the client to the server. Timings for every step
from request to response are shown as
different-colored bars, including DNS lookup, TCP
connection, SSL negotiation, back end response time,
and download time. The biggest takeaway
from the waterfall chart should be whether anything
low priority is happening during the critical path, or
the time during which the most important page
resources are loading. Looking at the
waterfall for the repeat view we configured
earlier, it should have much fewer requests. Most of the static resources
should be loaded from cache this time, so they
wouldn’t show up in the chart of
network activity. If you see any requests
highlighted in yellow with 304, this means that the browser
had incomplete information about the freshness
of the resource, and it needed to ask
the server if it could reuse what it has in cache. This is an inefficiency
that WebPagetest highlights to make it easier
to identify and optimize. Another really useful section of
the results is the film strip. You can see exactly how the
page UI was assembled onscreen and how long it took. You can even watch a replay
of the page load in real time or slow motion. But the best part is when you
do this for multiple tests, either an A/B test of the
same page or even competing websites. WebPagetest is an invaluable
and amazingly powerful tool. This is just a quick look
at some of its features, but there’s so much
more it can do, like controlling the test
with a scripting using the API and even hosting your
own private instance. You can learn more about all
of these features and more and the docs at bit.ly/wpt-docs. Thanks for watching, and
we’ll see you next time. [MUSIC PLAYING]

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