Documentation / Introduction
Sitespeed.io is a complete web performance tool that helps you measure the performance of your website. What exactly does that mean?
We think of a complete web performance tool as having three key capabilities:
- It should test web sites using real browsers, simulating real users connectivity and collect important user centric metrics like Speed Index and First Visual Render.
- It should analyse how your page is built and give feedback how you can make it faster for the end user.
- It should collect and keep data on how your pages are built so you can easily track changes.
What is sitespeed.io good for?
It is usually used in two different areas:
- Running in your continuous integration to find web performance regressions early: on commits or when you move code to your test environment
- Monitoring your performance in production, alerting on regressions.
To understand how sitespeed.io does these things, let’s talk about how it works.
First a few key concepts:
- Sitespeed.io is built upon a couple of other Open Source tools in the sitespeed.io suite.
- Browsertime is the tool that drives the browser and collect metrics.
- The Coach knows how to build fast websites and analyse your page and give you feedback what you should change.
- Visual Metrics is metrics collected from a video recording of the browser screen.
- Everything in sitespeed.io is a plugin and they communicate by passing messages on a queue.
When you as user choose to test a URL, this is what happens on a high level:
- sitespeed.io starts and initialises all configured plugins.
- The URL is passed around the plugins through the queue.
- Browsertime gets the URL and opens the browser.
- It starts to record a video of the browser screen.
- The browser accesses the URL.
- When the page is finished, Browsertime takes a screenshot of the page.
- It stops the video and closes the browser.
- Analyses the video to get Visual Metrics like First Visual Change and Speed Index.
- Browsertime passes all metrics and data on the queue so other plugins can use it.
- The HTML/Graphite/InfluxDB plugin collects the metrics in queue.
- When all URLs are tested, sitespeed sends a message telling plugins to summarise the metrics and then render it.
- Plugins pickup the render message and the HTML plugin writes the HTML to disk.
Now it’s time for you to install and run sitespeed.io.