How Accept-Version Headers Can Prevent Style Drift in Cached HTMX Fragments

Developers building HTMX applications often cache HTML fragments server-side to avoid costly backend queries, much like caching JSON responses in single-page applications. A common problem arises when CSS updates fail to reflect in cached fragments, causing visual inconsistencies across the app. A proposed solution uses two custom headers — Accept-Version sent by the frontend and Version returned by the backend — to negotiate which version of a resource is being requested and served. If the versions mismatch on a GET request, the backend triggers an HX-Redirect, forcing HTMX to reload the full page with the latest styles instead of serving a stale fragment. This lightweight content-negotiation approach requires every HTMX-enabled page to inject the current app version — such as a git commit SHA — into outgoing request headers via a small script.