How to Get Caching Strategy Right
Deciding what is stored, where, and for how long — in the browser, at a CDN edge, and inside the application — so repeated work is not repeated.
Marcus Adeyemi
Where most projects go wrong
The usual mistakes:
- Long cache lifetimes on URLs whose content changes
- Caching at the edge without checking for personalised content in the response
- Clearing the whole cache as the routine answer to any problem
- Multiple caching layers that nobody can reason about together
What good looks like instead
- Fingerprint static assets and cache them for a long time
- Keep HTML short-lived or revalidated so content changes appear
- Vary correctly on anything that changes the response, including compression and language
- Never cache a response that contains data belonging to one user
- Decide how each cache is cleared before you turn it on
Why it matters
Caching is the cheapest performance improvement available and the most dangerous when it is wrong, because a badly cached page serves one person's data to another.
The specs that matter
| Measure | Figure |
|---|---|
| Browser caching header | Cache-Control, with max-age and immutable for fingerprinted assets |
| Revalidation | ETag or Last-Modified, answered with 304 Not Modified |
| Fingerprinted asset practice | long max-age, because the filename changes when the content does |
| HTML practice | short or no-cache, because the URL does not change when the content does |
| The hard part | invalidation, not storage |
Knowing when to hand it over
Tip: Bring in help when stale content keeps reappearing after a publish, when a cache has leaked personalised data even once, or when several caching layers interact in ways nobody on the team can explain.
Where this comes from
- MDN Web Docs — HTTP caching
- Cloudflare Learning Center — What is caching
- RFC Editor — RFC 9111, HTTP Caching
The figures and practices above come from the sources listed.
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