cacheHints

A cache hint is a directive or piece of metadata that guides how a web resource should be cached by intermediaries such as proxies and content delivery networks (CDNs), as well as by the user's browser. These hints provide instructions on whether a resource is cacheable, for how long, and under what conditions it can be reused.

Cache hints are typically implemented through HTTP headers. For example, the Cache-Control header is a primary mechanism for specifying caching policies. Directives like `public`, `private`, `no-cache`, `no-store`, `max-age`, and `s-maxage` allow developers to fine-tune caching behavior. `max-age` indicates how many seconds a resource is considered fresh, while `s-maxage` is similar but specifically for shared caches like CDNs. `no-cache` means the resource must be revalidated with the origin server before being used, even if it appears fresh, whereas `no-store` prohibits caching altogether.

Other headers also contribute to cache hinting. The `Expires` header provides an absolute date and time after which the resource is considered stale, though `Cache-Control: max-age` is generally preferred as it is relative. `ETag` (Entity Tag) and `Last-Modified` headers are used for validation. When a cached resource is checked, these headers allow the browser or proxy to ask the server if the resource has changed without needing to download the entire resource again. This conditional request mechanism, using headers like `If-None-Match` (for ETags) or `If-Modified-Since` (for Last-Modified), can significantly reduce bandwidth usage and improve load times. Properly configured cache hints are crucial for optimizing website performance and reducing server load.