HTTP Caching — Cache-Control, ETags and Instant Repeat Visits

The fastest request is the one never made. Caching headers are how repeat visits become instant — and how sites accidentally serve stale files for a year.

The header

Cache-Control: max-age=31536000, immutable   # keep 1 year, never re-check
Cache-Control: no-cache                       # keep, but VALIDATE before using
Cache-Control: no-store                       # never keep (banking)

The strategy every real site uses

• HTML → no-cache: always validated, so users get new releases immediately
• CSS/JS/images → max-age=1 year + hashed filenames: app.3f2a9c.js — content change → new hash → new URL → cache "busted" naturally. Vite does the hashing automatically

This pair gives instant repeat loads AND instant deployments — no trade-off.

ETags — validation on the cheap

# first response:
ETag: "abc123"
# browser revalidates later:
If-None-Match: "abc123"
# server: 304 Not Modified (empty body — bytes saved)

Debugging

Network tab: "(disk cache)" = served locally, 304 = validated-unchanged, 200 with full size = cache miss. "Disable cache" checkbox while developing — half of all "my change isn't showing" mysteries end there. Your .htaccess Expires block (this site has one) is exactly these headers in Apache form.