What's the difference between Cache-Control: max-age=0 and no-cache?

Question

The header Cache-Control: max-age=0 implies that the content is considered stale (and must be re-fetched) immediately, which is in effect the same thing as

Answer 1

The difference is that no-cache (no-store on Firefox) prevents any kind of caching. That can be useful to prevent pages with secure content being written to disk and for pages that should always be updated even if they are re-visited with the back button.

max-age=0 indicates that a cache entry is stale and requires re-validation, but does not prevent caching. Often browsers only validate resources once per browser session, so the content may not get updated until the site is visited in a new session.

Usually, browsers will not delete expired cache entries, unless they are reclaiming the space for newer content when the browser cache is full. Using no-store, no-cache allows a cache entry to be explicitly deleted.