What is a Cache-Control header?

Cache-Control is an HTTP header that tells browsers and intermediary caches (like CDNs) how long to store a response and under what conditions to revalidate it. Common directives include max-age (how many seconds to cache), public/private (who can cache it), no-cache (always revalidate before using), and no-store (never cache at all).

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

no-cache does not mean 'do not cache' — it means 'cache the response, but always check with the server before using it'. no-store means 'never store this response anywhere'. Use no-cache for frequently updated pages where freshness matters. Use no-store for sensitive data like banking pages or private dashboards that should never be stored.

What does stale-while-revalidate do?

stale-while-revalidate=N tells the browser it can serve a stale (expired) cached response immediately while fetching a fresh copy from the server in the background. This improves perceived performance because the user sees content instantly without waiting for a network round-trip. After N seconds, the background refresh must complete before serving the cached version again.

When should I use immutable?

Use immutable together with a long max-age when you deploy assets with a content hash in the filename (e.g., main.a1b2c3d4.js). The immutable directive tells the browser the file will never change, so it can skip revalidation checks entirely during the cache lifetime. Without a hash-based filename, never use immutable — users would get stale files.

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

max-age controls caching in both browsers and shared caches (CDNs). s-maxage overrides max-age specifically for shared/proxy caches while leaving the browser max-age unchanged. This is useful when you want browsers to revalidate frequently but let your CDN cache responses for longer.

Free Developer Tool

Generate HTTP
Cache-Control Headers

Configure Cache-Control headers for HTML pages, JS/CSS bundles, images, fonts, and API responses. Get the exact directive string plus a plain-English breakdown of what each setting does.

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Resource Presets

Start from a sensible baseline for HTML, CSS/JS, images, fonts, or API responses — then fine-tune.

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Plain-English Explanations

Every directive gets a clear explanation of what it does and how browsers and CDNs interpret it.

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Server Config Examples

Get ready-to-paste Nginx and Apache configuration snippets alongside the header string.

1. Select Resource Type

HTML documents — usually stale-while-revalidate with short or zero max-age

2. Configure Directives

Cache Visibility

Any cache (browser, CDN, proxy) may store this response.

max-age (seconds)

0 seconds

s-maxage (CDN override)

Override max-age specifically for CDNs and shared proxies.

stale-while-revalidate

Serve stale content immediately while refreshing in the background.

Revalidate window (seconds)

stale-if-error

Serve stale content during origin server errors (5xx).

Error tolerance window (seconds)

immutable

Tells the browser this file will never change. Only use with content-hashed filenames.

must-revalidate

Force revalidation once stale — even if the server is unreachable.

3. Your Cache-Control Header

Header Value

Cache-Control: public, max-age=0, stale-while-revalidate=60, stale-if-error=86400, must-revalidate

Full Header Line

Cache-Control: public, max-age=0, stale-while-revalidate=60, stale-if-error=86400, must-revalidate

Plain-English Explanation

🌍 public — Any cache (browser, CDN, proxy) may store this response.
⏱️ max-age=0 — The response expires immediately. Must revalidate on every request.
⚡ stale-while-revalidate=60 (1m) — After max-age expires, the browser can serve the stale cached response immediately while fetching a fresh copy in the background. This eliminates latency for the user.
🛡️ stale-if-error=86400 (1d) — If the origin server returns a 5xx error, the stale cached response can be used for up to this long. Protects users during outages.
⚠️ must-revalidate — Once the response is stale, the browser must revalidate with the server before serving it. It cannot use a stale copy even if the server is unreachable.

Nginx

location ~* \.(js|css)$ {
  add_header Cache-Control "public, max-age=0, stale-while-revalidate=60, stale-if-error=86400, must-revalidate";
}

Apache

<FilesMatch "\.(js|css|png|jpg|woff2)$">
  Header set Cache-Control "public, max-age=0, stale-while-revalidate=60, stale-if-error=86400, must-revalidate"
</FilesMatch>

Frequently Asked Questions

Everything you need to know about HTTP Cache Headers Generator.

Generate HTTPCache-Control Headers