What is the difference between no-cache and no-store?

no-cache allows caching but requires revalidation before every use. no-store prevents any cache from storing the response at all.

What does immutable mean in Cache-Control?

immutable tells the browser the response will never change, so it should not revalidate even when the user hits reload. Best for versioned static assets.

What is stale-while-revalidate?

stale-while-revalidate allows serving a stale cached response while fetching a fresh copy in the background. This improves perceived performance.

What is the difference between max-age and s-maxage?

max-age applies to all caches including the browser. s-maxage overrides max-age for shared caches (CDNs and proxies) only.

Cache-Control Header Builder

What each cache will do

Browser (private cache)

Reuses it without contacting the server for 1 hour.

CDN / shared cache

Serves it from cache for 1 hour (from max-age).

Directives

Visibility · Who may store it

public refAny cache, including shared CDNs and proxies, may store the response (even if the request was authorized).

private refOnly the end user's browser may store it. Shared caches must not.

no-store refDo not write the request or response to any cache. The strongest opt-out; use for sensitive data.

Freshness · How long it is fresh

max-age refSeconds the response stays fresh. Applies to every cache; the browser uses only this.

seconds (1 hour)

s-maxage refLike max-age but for shared caches only; overrides max-age there.

Revalidation · When to re-check

no-cache refMay be stored, but must be revalidated with the origin before every reuse.

must-revalidate refOnce stale, never reuse without a successful revalidation (not even when the origin is unreachable).

proxy-revalidate refmust-revalidate, but only for shared caches.

immutable refThe body will never change while fresh, so browsers skip revalidation even on reload.

Stale · Serving old copies

stale-while-revalidate refAfter going stale, serve the stale copy for this many seconds while refreshing in the background.

stale-if-error refIf the origin errors (5xx or unreachable), serve the stale copy for this many seconds.

Other · Other

no-transform refIntermediaries must not alter the body (image recompression, minification).

Add it to your server

add_header Cache-Control "public, max-age=3600" always;

Cache-Control Builder