Every JavaScript byte is downloaded, parsed and executed on the main thread, so trimming the biggest bundles pays off twice.

CSS blocks rendering until it is downloaded and parsed, so the biggest files delay first paint the most.

Images are usually the easiest bytes to win back: resize them, compress harder or switch to a modern format like AVIF or WebP.

Web fonts often keep text invisible until they arrive. Subset the biggest ones or use font-display to show text earlier.

The HTML document is the first byte of everything: nothing starts rendering before it arrives.

The largest favicon files across the tested pages.

The largest JSON files across the tested pages.

The largest other files across the tested pages.

The largest SVG files across the tested pages.

The largest video files across the tested pages.

These assets took the longest time to download. Everything that waits for them (rendering, other requests on the same connection) is held up too.

Assets with a short cache time are re-downloaded by returning visitors. A longer cache lifetime makes repeat visits faster for free.