Cache-Control header for HTML

The Cache-Control header on the HTML. It decides how long browsers and CDNs may reuse the response instead of asking for it again.

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Cache-Control is the header that tells browsers, CDNs and proxies whether they may keep a copy of a response and for how long. Without it, each cache guesses on its own: some store the page for an unpredictable time, others ask for it again on every visit. Both are bad — the first can show visitors an outdated page after you publish a change, the second makes every visit download the full HTML.

How SiteScan checks it

The scanner reads the headers of the home page HTML and shows the Cache-Control value as it was sent. If there is a Cache-Control or at least an Expires header, the row is green: the server has made a decision. If neither is there, the row says “Missing” and turns amber. A deliberate no-store also counts as a decision.

What to send

For HTML that changes when you publish, a common choice is Cache-Control: no-cache together with an ETag or Last-Modified: the browser keeps a copy but checks with the server before each use, and gets a short 304 if nothing changed. For pages behind a CDN, s-maxage=300 lets the CDN hold the page for five minutes. Static files with a version hash in the name can be cached for a year: max-age=31536000, immutable. Details and examples are in the article on HTTP caching.