Chrome has a built-in utility to check performance and accessibility (and more) of your web app: Lighthouse Show archive.org snapshot .

UI/UX Design by

We make sure that your target audience has the best possible experience with your digital product. You get:

• Design tailored to your audience
• Proven processes customized to your needs
• An expert team of experienced designers

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Open the Develeoper Tools and go to the lighthouse tab:

Then you'll see some suggestions on how to improve your site.
This is cool, because you can even use it with non-public pages or your development environment (but be aware that some settings we're using for development, like not minifying JS and CSS files, might ruin your stats).

An alternative tool is Webpagetest Show archive.org snapshot .