Caching and CDNs

New idea

Why is the second visit faster?

Open a site for the first time and it might take 2 seconds. Open it again tomorrow and it can appear in half a second. The site didn't get faster. Your browser remembered.

The browser keeps copies of files it has already downloaded, like the logo, the CSS and the fonts. This store is the browser cache. The server says how long each copy stays fresh with a header such as Cache-Control: max-age=86400, counted in seconds. 86400 seconds is one day.

While a copy is fresh, the browser uses it straight from your device, with no request at all. The fastest request is the one you never send.