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Caching

Age

Indicates how long a response has been stored in a cache, in seconds since generation.

Syntax

Age: <seconds>

Example

Age: 3600

Description

Age indicates the time in seconds a response has been in a cache since the origin server generated it. Typically added by CDNs.

Combined with Cache-Control: max-age, clients can calculate remaining freshness lifetime.

Useful for debugging caching. If Age is always 0, the cache may not be working.

How real sites send this header

Home-page responses of 503 popular sites from the enterno.io /check catalogue, checked in the last 30 days.

27.0% (136 of 503) send Age.

See it on: cloudflare.com, cnn.com, docker.com, drupal.org, eff.org

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Related Headers

Cache-Control
The primary header for controlling caching behavior, defining how and for how long responses can be cached.
Expires
Specifies a date/time after which the response is considered stale. Superseded by Cache-Control max-age.
Pragma
Legacy HTTP/1.0 header for backward-compatible cache control. Replaced by Cache-Control.
Vary
Tells caches which request headers to consider when deciding whether to serve a cached response.

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