What third parties cost in load time

How it works

For every foreign domain the browser has to start from scratch: resolve the name, connect, encrypt, as described under server response time. Only then does the first file arrive. If the foreign server answers slowly or not at all, your page waits with it.

Then there is what the files do. Tracking, chat windows, advertising and embedded videos often bring a lot of JavaScript, which competes for the same main thread as your page.

bytereport counts the foreign domains that appear in the HTML: in scripts, stylesheets, images, preloaded fonts and iframes. Subdomains count together, so www.googletagmanager.com and googletagmanager.com are one. Subdomains of your own domain such as cdn.example.com count as your own. Up to three foreign domains is good, more than eight counts as poor. Whatever a script loads later is not included; in practice there are usually more.

What matters

• Remove what nobody looks at. Old tracking pixels and forgotten tags in the tag manager cost time on every page view.
• Serve it yourself. Fonts and libraries such as jQuery can be loaded from your own domain, see web fonts.
• Embeds only after a click. Videos and maps show a preview image first and only load when someone starts them. This saves time and is needed for data protection too, see external content.
• Load late. Third-party scripts get async or defer, see render-blocking resources.
• Prepare the connection. For the two or three most important domains that stay, preconnect starts the connection earlier:

<link rel="preconnect" href="https://cdn.example.net">

How to set it up

Which services are included is usually known to marketing and the agency. Go through the list in the details with them and ask of each domain who needs it. Tags are removed in the tag manager; click-to-load embeds are offered by many consent tools and CMS plugins.