Age Header

What is the Age header?

The Age response header, defined in RFC 9111, gives the estimated number of seconds that have elapsed since the response was produced by the origin server. It is added by caches and CDNs, so its presence usually means the response was served from a cache rather than freshly generated.

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: A large Age value confirms a request was satisfied by a CDN edge, which is useful when debugging why clients are seeing stale data.

Examples

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