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Auditing Performance

Why and what?

You've probably heard about all the good things that Progressive Web App techniques can do for your site. You might feel tempted to jump straight in and add PWA features. That's possible, but you'll be much better off if you get 'PWA-ready' first.

No amount of PWA magic will fix problems such as blocking JavaScript or bloated images. PWAs need a solid foundation.

So how do you check the health of your website? The first step is to do a site audit: an objective review of what works well and where (and how) there could be improvement.

Auditing your site or app will help you build a resilient, performant experience — and highlight quick wins that can be implemented with minimal sign-off. An audit also gives you a baseline for data-driven development. Did a change make things better? How does your site compare with competitors? You get metrics to prioritize effort, and concrete evidence to brag about once you've made improvements.

If you only have 5 minutes...

Run Lighthouse on your homepage and save the report data. You get a quantified baseline and a todo list for improvements to performance, accessibility, security and SEO.

If you only have 30 minutes...

Lighthouse is probably still the best place to start, but with a little more time you can also record results from other tools:

  • Chrome DevTools Security panel: HTTPS usage.
  • Chrome DevTools Network Panel: load timings; resource sizes and number of requests for HTML, CSS, JavaScript, images, fonts and other files.
  • Chrome Task Manager: if your site constantly uses significant CPU or more memory than other apps then you may need to fix memory leaks, task running or resource loading problems. Make sure to test your site on devices representative of your users.
  • WebPagetest: performance for different locations and connection types, caching, time to first byte, CDN usage.
  • Pagespeed Insights: load performance, data cost and resource usage, including Chrome User Experience report data highlighting real-world performance statistics.
  • Speed Scorecard and Impact Calculator: compare site speed against peers and estimate the potential revenue opportunity of improving site speed.

Make sure to test your website as a first-time user sees it. Open the site an Incognito (Private) Window, or use browser tools to disable caching and clear storage. This ensures that every asset is retrieved from the network and not from a local cache, so you get an accurate picture of first-load performance.

WebPagetest is a free service that runs performance tests from multiple locations globally using real browsers with real connections, to provide detailed metrics and optimization advice.
  • Leverage webpagetest.org/easy to quickly simulate differences between network connection types on mobile
  • Generate a Lighthouse audit and report with every WebPagetest trace.
  •  Measure site on first visit as well as for repeat views — for example: to see how much service worker caching helps.
  • Visually compare multiple sites and get filmstrip and waterfall comparisons.

Nothing beats real world testing — try out your site with the same devices and connectivity as your users and keep a record of your subjective experience.

If you find the range of tools bewildering...

Take a look at our guide: How To Think About Speed Tools.

If nothing else, simply use Lighthouse to check for:

Audience, stakeholders, context

Priorities for refactoring depend on your audience, content and functionality. Who visits your site? Why and how do they use it? What's your performance budget? If you're not sure of the answer to these questions, try the requirements gathering exercises from our PWA training resources: Your audience, your content and Design for all your users.

Who are your stakeholders, and what are their priorities? This will affect the way you structure, present and share your audit data.

If you can't audit your whole site, check page analytics to get an idea of where to focus. High bounce rates, low time-on-page and unexpected exit pages can be a good indicator of where to begin. Likewise business metrics such as hosting costs, ad clicks and conversions. Get an overview from stakeholders of what data matters to them.

Test, record, fix, repeat

Record the state of your site before making any changes, to uncover problems and set a starting point for improvements or regressions. That gives you data to justify and reward development effort.

Make sure to test multiple page types within your site — not just the home page. For single page apps, test different components, routes and UX flows, and not just the first load experience.