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15 – Performance (Sitespeed.io)

The test starts a real browser, loads the page and measures what actually happens. It's a measurement, not an estimate derived from file sizes.

What is tested?

  • Load time: how long it takes before the page is usable
  • Number of requests: how many files the browser has to fetch

The tool behind it is Sitespeed.io, which runs the page several times and uses the median, so that a single slow run doesn't decide the score.

How it affects the score

The score reflects how the page is experienced:

Score Meaning
5.0 The website is really fast
4.0 The website is fast
3.0 About average speed
2.0 The website is quite slow
1.0 The website is very slow

The number of requests is weighed in separately. Many small files cost time even when each one is small.

Running the test 

python default.py -u https://example.com -t 15 -r

Settings

Setting Default Meaning
tests.sitespeed.browser chrome Browser, chrome or firefox
tests.sitespeed.iterations 2 Number of runs the median is taken over
tests.sitespeed.timeout 30 Seconds before a run is aborted
tests.sitespeed.mobile false Simulate mobile. Can also be enabled with the -m flag
tests.sitespeed.docker.use false Run Sitespeed.io in Docker rather than via Node
tests.sitespeed.xvfb false Run the browser on a virtual display, for servers without graphics

Worth knowing

Several tests share a single Sitespeed run. Running 15 together with, say, 21, 22 and 23 is faster than running them separately.

See also