RFC 9111 Aligned — Production-Grade HTTP Caching

Master HTTP Caching —
From RFC to Production

Design, debug, and optimize HTTP caching strategies across browsers, CDNs, and origin servers. Bridge the gap between specification and real-world deployment.

Core Fundamentals Cache-Control Directives CDN & Edge Strategies Validation & ETags

HTTP caching is the single most impactful performance optimization available to modern web infrastructure. When implemented correctly — with precise Cache-Control directives, correct Vary headers, and well-designed invalidation strategies — caching eliminates redundant origin fetches, reduces TTFB to single-digit milliseconds, and keeps your infrastructure resilient under load.

This site translates RFC 9111 into concrete engineering patterns. Every directive, every header interaction, and every edge-routing decision is documented with production-grade examples, curl diagnostics, and CDN-specific behavior matrices. Whether you're debugging a cache miss, designing a multi-tier invalidation strategy, or aligning your ETag implementation with browser behavior, you'll find authoritative, RFC-aligned answers here.

From browser private caches and CDN shared caches to stale-while-revalidate patterns and tag-based purge workflows — this is the definitive reference for engineers who treat caching as a first-class architectural concern.

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Start Here

01
Cache Hit, Miss & Bypass Mechanics Understand the three outcomes of every HTTP cache lookup and when each fires.
02
Freshness vs Validation Models Learn how max-age freshness and ETag/Last-Modified conditional requests differ.
03
Mastering max-age and s-maxage Configure browser vs shared-cache TTLs correctly — with real header examples.
04
no-cache vs no-store The most misunderstood directive pair — clarified with concrete use cases.
05
How CDN Cache Keys Work What CDNs include in the cache key and how it drives hit rates.
06
Origin Shielding & Request Collapsing How CDNs protect origins from thundering-herd cache misses.
Explore the Guides

Four Deep-Dive Sections

Core Caching Fundamentals & HTTP Lifecycle

Master RFC 9111 mechanics — freshness calculation, validation flows, cache hierarchy, and the complete HTTP request lifecycle from browser to origin.

Cache-Control Directives & Header Combinations

Deep-dive into directive taxonomy, precedence rules, and safe combination patterns. Learn to configure max-age, s-maxage, no-cache, and immutable without ambiguity.

CDN Architecture & Edge Routing Strategies

Navigate CDN cache key generation, Vary header routing, origin shielding, request collapsing, and tag-based purge workflows at scale.

Cache Validation & Conditional Requests

Keep caches correct without wasted bandwidth. Master ETag and Last-Modified validators, If-None-Match conditional requests, 304 responses, and stale-while-revalidate.

Go Deeper

Featured Guides

Core Fundamentals How to Calculate Cache Freshness Lifetime Step-by-step RFC 9111 freshness calculation: max-age, Age, and heuristic TTLs. Core Fundamentals When Does a Browser Invalidate a Cached Resource? Explicit TTL expiry, user navigation triggers, and forced revalidation explained. Directives How to Combine Cache-Control Directives Safely Which directive pairs are safe, which conflict, and how to verify the result with curl. Directives What Happens When max-age Expires Stale detection, conditional revalidation, and the role of stale-while-revalidate. CDN & Edge How to Debug CDN Cache Key Mismatches Diagnose low hit rates caused by unexpected cache key fragmentation across major CDNs. CDN & Edge Using Vary: Accept-Encoding Without Fragmenting Cache Safe Vary patterns that maximize compression support without blowing up cache cardinality. Directives Cache-Control Best Practices for REST APIs Recommended directive sets for JSON endpoints, versioned resources, and authenticated responses. Core Fundamentals Understanding HTTP/1.1 vs HTTP/2 Caching Rules Where the caching semantics are identical and where HTTP/2 push and multiplexing change the picture. Validation & ETags ETag vs Last-Modified: Which Validator to Use A decision guide comparing precision, cost, and precedence when both validators are present. Validation & ETags How to Debug 304 Not Modified Responses Why revalidation returns 200 instead of 304 — and how to trace it back to the validator. CDN & Edge Surrogate-Key vs Cache-Tag Across CDN Vendors How Fastly, Cloudflare, and Varnish differ in tag syntax, limits, and purge APIs. Core Fundamentals Interpreting X-Cache and CF-Cache-Status Headers Full value tables for every major CDN's cache-status header, and how to read them.