This reference explains the HTTP caching headers that control how browsers and CDNs store responses — Cache-Control directives, ETag, Last-Modified and more.
| Header / directive | Meaning |
|---|---|
| Cache-Control: max-age=N | Cache for N seconds |
| Cache-Control: no-cache | Revalidate before using |
| Cache-Control: no-store | Never cache |
| Cache-Control: public | Any cache may store it |
| Cache-Control: private | Only the browser may cache |
| Cache-Control: immutable | Never changes — skip revalidation |
| ETag | Version identifier for a resource |
| Last-Modified | When the resource last changed |
| Expires | Absolute expiry date (legacy) |
| Age | Seconds since cached |
| Vary | Which request headers affect caching |