Topic
Caching
Learn how browsers and intermediaries store, validate, and reuse HTTP responses with cache directives, validators, and conditional requests.
- HTTP Status Codes
203 Non-Authoritative Information
203 means a proxy modified the origin response before passing it on. Learn when it is sent, how it differs from 200, caching rules and what clients should do.
- Comparisons
301 vs 302 Redirects
Understand the difference between 301 Moved Permanently and 302 Found redirects. Learn when to use each, how browsers cache them, and their SEO implications.
- Comparisons
301 vs 308: Permanent Redirects and POST Requests
301 vs 308: both signal a permanent move, but only 308 preserves POST. Compare browser handling, Google indexing, cache controls, and curl traces.
- HTTP Status Codes
304 Not Modified
Cached response is still valid. Learn how 304 Not Modified improves performance through conditional requests and caching.
- Comparisons
304 Not Modified vs 200 OK
When a server answers 304 Not Modified instead of 200 OK, and how conditional requests with ETag and Last-Modified save bandwidth on revalidation.
- HTTP Headers
Age Header
Learn how the Age header indicates how long a response has been cached in seconds. Understand cache freshness calculations and CDN behavior.
- HTTP Headers
Cache-Control Header: Directives, Examples and CDN Behavior
Cache-Control directives explained: max-age, no-cache vs no-store, s-maxage, stale-while-revalidate, immutable, with nginx, Cloudflare and Next.js examples.
- Comparisons
Cache-Control: no-cache vs no-store
Compare the no-cache and no-store Cache-Control response directives and choose the correct policy for sensitive or frequently changing responses.
- Glossary
CDN (Content Delivery Network)
A CDN is a network of edge servers that cache and serve responses near users. See how cache hits show up in headers and what CDNs do not cache by default.
- Debug Guides
CDN Not Caching: cf-cache-status DYNAMIC, BYPASS, MISS
CDN not caching? Read cf-cache-status DYNAMIC, BYPASS, MISS or X-Cache: Miss from cloudfront, then fix Set-Cookie, Cache-Control, Vary and cache keys.
- Guides
Content Negotiation: Accept, Languages and Caches
Implement HTTP content negotiation with Accept headers, q-values, Vary and 406 responses, with Express, Django and nginx examples and language SEO guidance.
- HTTP Headers
ETag Header: Strong vs Weak, If-None-Match and 304 Debugging
ETag identifies a resource version for cache validation and optimistic locking. Strong vs weak ETags, If-None-Match, If-Match, and why nginx gzip weakens them.
- Comparisons
ETag vs Last-Modified: HTTP Cache Validators
ETag vs Last-Modified: strong and weak validation, one-second timestamps, conditional request precedence, multi-server consistency, and CDN debugging.
- HTTP Headers
Expires Header
Learn how the Expires header specifies when cached responses become stale. Understand date formats and when to use Expires vs Cache-Control for caching.
- Comparisons
GET vs POST
Understand the fundamental differences between GET and POST HTTP methods. Learn about safety, idempotency, caching, request bodies, and when to use each.
- Guides
HTTP Headers and Caching: A Practical Guide
Master HTTP caching with Cache-Control, ETag, Last-Modified, and conditional request headers. Learn how to optimize performance with proper cache strategies.
- HTTP Headers
If-Modified-Since Header
Learn how the If-Modified-Since header requests resources only if modified since a specific date. Reduce bandwidth with efficient conditional caching.
- HTTP Headers
If-None-Match Header
Learn how the If-None-Match header makes conditional requests using ETags. Avoid downloading unchanged resources and reduce bandwidth with cache validation.
- HTTP Headers
If-Unmodified-Since Header
Learn how the If-Unmodified-Since header makes requests conditional on resources not being modified. Prevent conflicts in concurrent update scenarios.
- HTTP Headers
Last-Modified
Learn how the Last-Modified header indicates when a resource was last changed. Enable efficient cache validation with If-Modified-Since conditional requests.
- HTTP Headers
Vary Header: Cache Keys, Vary: Origin and Accept-Encoding
Vary lists the request headers a response depends on, so caches keep separate copies. Vary: Accept-Encoding, Vary: Origin for CORS, Vary: *, and CDN cache keys.
- HTTP Headers
Warning Header
Learn about the deprecated Warning header that provided additional status information about message transformations. Understand why it was removed from HTTP.
More topics
- 63 pages
Security
Study HTTP security controls for transport, cookies, browser isolation, authentication, content policy, and response hardening.
- 24 pages
Performance
Improve HTTP delivery with caching, compression, connection reuse, timing signals, and response metadata.
- 22 pages
Cookies
Understand cookie storage, scope, transport, expiration, and security across HTTP headers, attributes, and session flows.
- 22 pages
CORS
Trace cross-origin browser requests, preflight exchanges, response headers, credentials, and common CORS failure modes.