maxage

Maxage, in the context of HTTP caching, refers to the max-age directive used in the Cache-Control header to specify how long a cached response is considered fresh. The directive takes the form max-age=<seconds>, where <seconds> is a non-negative integer representing the time, in seconds, that the response may be served from cache without contacting the origin server.

When a response includes both Expires and Cache-Control headers, max-age generally takes precedence for modern HTTP caches. The s-maxage directive can override max-age for shared caches (such as intermediate proxies), while private caches use max-age. A value of 0 means the response is immediately stale and will typically require revalidation with the origin server before reuse.

Cache-Control directives such as public or private indicate whether a response may be cached by shared caches or only by the end user’s browser. The max-age value is commonly used for static resources (images, scripts, stylesheets) to improve performance and reduce server load, while dynamic content often uses shorter max-age values or no-store to prevent caching.

Behavior and considerations: browsers and intermediary caches store a response for the duration specified by max-age. If the resource changes before the max-age expires, developers may need to implement cache-busting techniques (e.g., versioned URLs) or use no-cache/no-store for sensitive content. After a response becomes stale (age exceeds max-age), caches generally revalidate with the origin server before serving the content, unless configured otherwise.

Max-age is defined in HTTP/1.1 semantics (RFC 7234). It is a central tool for controlling freshness, cache efficiency, and bandwidth usage in web architectures.