Caching

htmx works with standard HTTP caching mechanisms out of the box.

If your server adds the Last-Modified HTTP response header to the response for a given URL, the browser will automatically add the If-Modified-Since request HTTP header to the next requests to the same URL.

For polling use cases where you want the server to skip responses when content hasn’t changed, see the ptag extension.

Be mindful that if your server can render different content for the same URL depending on some other headers, you need to use the Vary response HTTP header.

For example, if your server renders the full HTML when the HX-Request header is missing or false, and it renders a fragment of that HTML when HX-Request: true, you need to add Vary: HX-Request. That causes the cache to be keyed based on a composite of the response URL and the HX-Request request header rather than being based just on the response URL.