Age

What is the Age header?

The Age response header, defined in RFC 9111, gives the sender’s estimate, in seconds, of the time since the response was generated or successfully validated at the origin server. It is added by caches and CDNs. RFC 9111 states that its presence implies the response was not generated or validated by the origin for this request, but the reverse does not hold: a response without Age may still have come from a cache that does not send it.

API Usage & Best Practices

• Estimate freshness: Comparing Age against the freshness lifetime from Cache-Control: max-age tells you how much of a cached response’s usable life remains.
• Diagnose caching: Any Age value, including 0, means some cache on the path answered the request, which is useful when debugging why clients are seeing stale data. It does not say which cache; use Cache-Status for that.

Examples

HTTP/1.1 200 OK
Cache-Control: max-age=3600
Age: 118