◆Error Codes Wiki

HTTP Caching Headers — Cache-Control, ETag, and Expires Explained

Informational2xx success

Overview

Complete guide to HTTP caching headers including Cache-Control directives, ETag validation, Expires headers, and troubleshooting stale cache issues.

Key Details

  • Cache-Control is the primary header for controlling caching behavior in HTTP/1.1+
  • Common directives: max-age, no-cache, no-store, public, private, must-revalidate
  • ETag provides content-based cache validation — the server returns 304 Not Modified if content unchanged
  • Last-Modified/If-Modified-Since provides time-based cache validation
  • Expires header is the older HTTP/1.0 approach — Cache-Control takes precedence when both are present

Common Causes

  • Stale content served from cache due to overly long max-age values
  • no-cache misunderstood — it means 'revalidate before using cache', not 'do not cache'
  • CDN caching old content after server-side updates
  • Browser serving cached responses for dynamic content that should be fresh

Steps

  1. 1Set Cache-Control: no-store for sensitive data (banking, medical) to prevent any caching
  2. 2Use Cache-Control: public, max-age=31536000 for static assets with content hashes in filenames
  3. 3Implement ETag headers for dynamic content that changes infrequently
  4. 4Use Cache-Control: no-cache for content that should always be revalidated before display
  5. 5Add Vary header when response differs by Accept-Encoding, Accept-Language, or other request headers
  6. 6Purge CDN cache after deployments: use your CDN's purge API or deploy with new asset URLs

Tags

cache-controletagexpireshttp-cachingcdn-cache

Related Items

http-304-not-modifiedhttp-200-okhttp-206-partial-content

More in 2xx Success

http-200-okHTTP 200 OK — What It Means & How to Fix It
Informational
http-201-createdHTTP 201 Created — What It Means & How to Fix It
Informational
http-202-acceptedHTTP 202 Accepted — What It Means & How to Fix It
Informational
http-203-non-authoritative-informationHTTP 203 Non-Authoritative Information — What It Means & How to Fix It
Informational
http-204-no-contentHTTP 204 No Content — What It Means & How to Fix It
Informational
http-205-reset-contentHTTP 205 Reset Content — What It Means & How to Fix It
Informational

Frequently Asked Questions

no-cache allows caching but requires revalidation with the server before each use. no-store prohibits caching entirely — nothing is stored on disk or in memory.