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How To Test Page Speed With Google Lighthouse

· 3 min read

Lighthouse is a free tool developed by Google that analyzes your website and generates a report on your page speed, accessibility, and SEO.

All you need to do is provide your website URL and Lighthouse automatically runs through a large number of individual checks (called audits). You can see how well you do on each audit and what you can do to improve.

This article looks at the different options you have for running Lighthouse what the differences are between them.

Lighthouse test report

Run Lighthouse on PageSpeed Insights

The easiest way to run Lighthouse is to use Google's official PageSpeed Insights tool that's built on top of Lighthouse.

Enter your website URL and click Analyze to start your page speed test. PageSpeed Insights can run tests from four different test locations and automatically selects the one that's closest to you.

PageSpeed Insights homepage

Once your test is complete you will find real user data from Chrome User Experience Report (CrUX) at the top of the page.

Below that you find the Lighthouse report under the "Diagnose performance issues" section.

Lighthouse report on PageSpeed Insights

The top of the Lighthouse report provides a high-level Performance score. Below that you can find the individual opportunities for optimization ranked by estimated impact.

Lighthouse recommendations

Run Lighthouse in Chrome DevTools

Lighthouse is directly integrated into Chrome's developer tools. Simply open the developer tools (via right-click + Inspect) and then select the Lighthouse tab.

Running Lighthouse from Chrome DevTools

Running Lighthouse in DevTools offers more configuration options. For example you can select either the default simulated throttling or DevTools throttling. To view this setting, first click on the gear icon in the top right. DevTools throttling takes a bit longer but usually provides more reliable data.

DevTools throttling options

Run Lighthouse on DebugBear

DebugBear offers a free website speed test that's built on top of Lighthouse. In addition to running Lighthouse the tool also collects real user CrUX data and provides custom reports.

You'll also get the most reliable lab data as DebugBear uses realistic packet-level throttling.

DebugBear test result

Run Lighthouse with the CLI

Lighthouse offers a feature-rich command line interface (CLI). If you already have Node.js installed on your computer you can run npm install lighthouse -g to globally install Lighthouse on your device.

Then run a Lighthouse test like this:

lighthouse --view

The --view option means that Lighthouse will automatically open the generated HTML report in the browser for you to see.

As Lighthouse is running the test you can see each step that it takes.

Lighthouse CLI output

You can pass in various advanced options, for example the throttling method or the network round trip time (RTT). In the example below we use an RTT of 5 seconds, so the test result will be extremely slow.

lighthouse --view \ 
--throttling-method devtools \
--throttling.rttMs 5000

Run lighthouse --help to get an overview of all available options.

Monitor your Lighthouse scores over time

Depending on how you run your Lighthouse test you have different configuration options and get data of different quality. DebugBear can monitor your Lighthouse scores over time and provide high-quality page speed metrics.

DebugBear Lighthouse score dashboard

Monitor Page Speed & Core Web Vitals

DebugBear monitoring includes:

  • In-depth Page Speed Reports
  • Automated Recommendations
  • Real User Analytics Data

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