About

About CacheLens

A free, no-sign-up tool that turns a response's caching headers into a clear answer: will it be cached, by whom, for how long, and what's wrong with it.

Caching headers are deceptively tricky. max-age and s-maxage apply to different caches; no-cache does not mean "don't cache"; private silently disables your CDN; a missing validator quietly turns every refresh into a full refetch. CacheLens parses Cache-Control, Expires, Date, Age, ETag, Last-Modified, Vary and Pragma and explains the browser and shared-cache outcome side by side.

How it works

The analysis follows the response-side rules of RFC 9111 (HTTP Caching): storability, freshness lifetime (s-maxage → max-age → Expires−Date), revalidation, and validators. Everything runs in your browser — no request is made and nothing you paste is stored or sent.

What it is not

It is a static read of the headers you provide. Real-world behavior also depends on the HTTP method, the status code, request headers such as Authorization, and each cache's configuration. Treat the output as a fast sanity check, not a guarantee.