DNS & Glossary

HTTP caching

How browsers and CDNs store and reuse responses to avoid redundant round trips — governed by Cache-Control freshness and ETag/Last-Modified revalidation.

What it is

Caching has two layers: freshness (Cache-Control: max-age, public/private, immutable) decides how long a response can be reused without asking, and revalidation (ETag / If-None-Match, Last-Modified) confirms a stale copy is still good with a cheap 304. Correct headers cut latency and origin load dramatically.

HTTP RESPONSE HEADERS
Cache-Control: public, max-age=31536000, immutable   # fingerprinted asset
Cache-Control: private, no-cache                      # revalidate every time

Why it matters

  • Good caching is one of the biggest wins for performance and cost.
  • It is essential to CDN effectiveness.

Common mistakes

  • Caching private, user-specific responses publicly, leaking data across users.
  • No caching on static, fingerprinted assets, forcing needless re-downloads.

How WebInspect checks this

  • WebInspect reports Cache-Control, ETag, Age and CDN cache behaviour and explains the effective caching in plain English.