Immutable cache (versioned assets)
When a CSS or JS file contains a hash in its name (e.g. main.abc123.js), this guarantees the name changes with each new version. The immutab…
Analyse my site for freeHow TheSiteFuse checks "Immutable cache (versioned assets)"
When a CSS or JS file contains a hash in its name (e.g. main.abc123.js), this guarantees the name changes with each new version. The immutable attribute in Cache-Control tells the browser: "This file will never change — cache it forever without ever re-checking". This is different from simple max-age which still triggers re-validations.
Real-world impact of "Immutable cache (versioned assets)"
Without immutable, even with a long max-age, the browser may still send a conditional request (If-None-Match) to check if the file changed. With immutable, these re-validations never happen. For versioned assets, it's the most efficient cache setting.
Does your site pass this check?
Run the free full audit (120 checks) and instantly discover what needs fixing.