api: YAML JSON TOON Database
version: 1.0.0
format: toon
dataset:
  id: 2808
  slug: http-caching-guide
  title: "HTTP Caching: Complete Guide"
  description: "HTTP caching strategies: Cache-Control directives, ETag/Last-Modified validation, CDN caching, stale-while-revalidate, and browser cache behavior."
  summary: "A guide to HTTP caching directives and validation: Cache-Control values such as max-age, no-cache, no-store, private, public and immutable, and the validators ETag and Last-Modified, each with an example and notes on when it applies."
  use_when[2]: You are setting caching headers for static assets or API responses.,You need to explain the difference between no-cache and no-store.
  caveats[2]: no-cache does not mean 'do not cache'; it means revalidate before reuse. no-store is the directive that forbids storing.,"Shared caches such as CDNs and browser caches have different rules (s-maxage, private)."
  related[4]: http-response-headers,http-request-headers,http-redirect-status-codes,http-content-negotiation
  entry_count: 12
  fields[10]{section,field,type,example}:
    directives,directive,string,max-age=<seconds>
    directives,type,string,Freshness
    directives,description,string,How long the resource is considered fresh from …
    directives,example,string,"Cache-Control: max-age=31536000 (1 year, for im…"
    directives,notes,string,Relative to request time; use long values for v…
    validation,mechanism,string,ETag
    validation,header,string,"ETag: \"abc123\""
    validation,description,string,Opaque identifier for a specific version of a r…
    validation,example,string,"Client sends If-None-Match: \"abc123\"; server re…"
    validation,notes,string,Strong ETags guarantee byte-for-byte identity; …
  category: HTTP Status Codes
  category_slug: http-status-codes
  tags: "http,caching,cache-control,etag,cdn,performance,browser-cache"
  view_count: 39
  created_at: 1778695229
  updated_at: 1778695229
data:
  directives[10]{directive,type,description,example,notes}:
    max-age=<seconds>,Freshness,How long the resource is considered fresh from the time of the request,"Cache-Control: max-age=31536000 (1 year, for immutable assets)",Relative to request time; use long values for versioned static assets
    s-maxage=<seconds>,Freshness (shared caches),"Like max-age but only for shared caches (CDNs), overrides max-age for shared caches","Cache-Control: s-maxage=3600, max-age=0",CDNs respect s-maxage; browsers ignore it and use max-age
    no-cache,Revalidation,Resource can be cached but must revalidate with origin server before use,"Cache-Control: no-cache",Does NOT mean 'don't cache' — it means 'check with server first'
    no-store,No caching,"Do not store in any cache (browser, CDN, proxy)","Cache-Control: no-store","Use for sensitive data (banking, personal info) or highly dynamic content"
    private,Cache scope,"Only cacheable by browser (private cache), not by CDNs/proxies","Cache-Control: private, max-age=3600",Default for authenticated responses; use public for CDN-cached content
    public,Cache scope,Cacheable by any cache including shared CDNs and proxies,"Cache-Control: public, max-age=86400",Required for CDN caching of content behind auth (with care)
    must-revalidate,Revalidation,"Once stale, the cached response cannot be used without successful revalidation","Cache-Control: max-age=3600, must-revalidate",Prevents serving stale content even when offline
    stale-while-revalidate,Stale handling,Serve stale content while fetching fresh version in background,"Cache-Control: max-age=3600, stale-while-revalidate=86400","Improves perceived performance; user gets instant response, fresh content loads async"
    stale-if-error,Error fallback,Serve stale content if origin server returns 5xx error,"Cache-Control: stale-if-error=604800",Graceful degradation during origin outages; use with monitoring
    immutable,Freshness optimization,Resource will never change; browser skips revalidation checks even on user reload,"Cache-Control: max-age=31536000, immutable",Only for versioned assets (app.abc123.js); prevents unnecessary revalidation on reload
  validation[2]{mechanism,header,description,example,notes}:
    ETag,"ETag: \"abc123\"","Opaque identifier for a specific version of a resource, compared via If-None-Match","Client sends If-None-Match: \"abc123\"; server responds 304 Not Modified if unchanged",Strong ETags guarantee byte-for-byte identity; weak ETags (W/) allow semantic equivalence
    Last-Modified,"Last-Modified: Wed, 21 Oct 2024 07:28:00 GMT","Timestamp of last modification, compared via If-Modified-Since","Client sends If-Modified-Since: <date>; server responds 304 if not modified",1-second resolution; ETag is more precise and preferred for programmatic use