Storing files on the visitor's device.
WHAT IT DOES
Tells the visitor's browser to keep files it already downloaded: images, styles, scripts.
On the next visit, those load instantly from the device rather than being downloaded again.
WHY IT MATTERS
Returning visitors experience a much faster site.
It also saves them data, which matters on mobile.
HOW TO ENABLE IT
Caching plugins handle it.
It can also be set in .htaccess, which any developer can do.
WHAT TO CACHE AND FOR HOW LONG
- Images and fonts: a long period, since they rarely change
- Styles and scripts: a shorter period, or versioned filenames
- HTML: short or not at all, since content changes
THE UPDATE PROBLEM
If a file is cached for a year and you change it, returning visitors see the old version.
Good systems add a version to the filename so changes are picked up.
HOW TO CHECK
Load your site, then load it again. The second load should be noticeably faster.
