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HTTP Header
Age
CachingIndicates the number of seconds a cached response has been stored in a proxy cache.
HTTP header reference, syntax, examples, and developer usage.
What is the Age header?
The Age HTTP header is used to transmit metadata between a client and server as part of HTTP requests or responses.
HTTP headers define how content should be interpreted, cached, authenticated, secured, or processed by browsers and APIs.
Direction
This header may appear in both HTTP requests and responses.
Syntax
Age: <delta-seconds>
Example
Age: 3600
Common use cases
- Determining how long a response has been in a CDN or proxy cache
- Debugging caching behavior in multi-layer architectures
- Calculating remaining freshness alongside Cache-Control max-age
Common mistakes
- Using the header in the wrong request or response context
- Sending invalid header values
- Incorrect header syntax
- Assuming the header automatically changes server behaviour
Practical developer insight
Age is added by caches, not origin servers. A value of 0 means the response was just fetched from the origin. To determine if a response is still fresh, compare Age against the max-age directive in Cache-Control. If Age >= max-age, the response is stale and the cache should revalidate.