CODEWITHSUNDEEP
http-headerscache-control
whiterose
whiterose

Reputation: 4711

what’s the difference between Expires and Cache-Control headers?

What’s the difference between Expires and Cache-Control headers?

Upvotes: 230

Views: 86698

Answers (7)

A Lee
A Lee

Reputation: 8066

They can both be used to control the lifetime of a cached response but Cache-Control, introduced in HTTP/1.1, offers many more features and should generally be favored over Expires, defined in HTTP/1.0.

In modern browsers a Cache-Control: max-age or Cache-Control: s-maxage directive will also override any Expires header in the response.

As a concrete example, Cache-Control: max-age=604800 indicates the number of seconds that the given HTTP response should be considered fresh. In other words, the response should be considered stale and evictable from the cache 604800 seconds (7 days) after the HTTP response was generated.

Expires uses explicit datetime strings like "Friday, 28 Feb 2020 20:20:20 GMT" and is obviously more challenging to parse (and generate!) than a simple number of seconds integer.

Other good resources for understanding how HTTP caching works:

Upvotes: 152

Rob
Rob

Reputation: 19

Except for the private/public options of CC, I can't see any difference. When using Expires like "access plus 1 year/month/week/day", it works in exactly the same way as CC does.

Upvotes: 0

ray
ray

Reputation: 171

If you are still interested, I leave this recommendation directly from google's boys. https://developers.google.com/speed/docs/insights/LeverageBrowserCaching They prefer Expires before than Cache-Control

Upvotes: -1

nodejh
nodejh

Reputation: 8008

Cache-Control was defined in HTTP/1.1, tells all caching mechanisms from server to client whether they may cache this object. It is measured in seconds: Cache-Control: max-age=3600.

The Expires header field gives the date/time after which the response is considered stale. The Expires value is an HTTP-date timestamp: Expires: Tue, 18 Jul 2017 16:07:23 GMT.

If a response includes a Cache-Control field with the max-age directive, a recipient MUST ignore the Expires field.

Upvotes: 12

Devi
Devi

Reputation: 5453

Heroku devcenter has an excellent article on this subject.

Quoting from it,

While the Cache-Control header turns on client-side caching and sets the max-age of a resource, the Expires header is used to specify a specific point in time the resource is no longer valid.

Upvotes: 4

Paul
Paul

Reputation: 20091

According to this Google Developers article, HTTP Caching:

Cache-Control header was defined as part of the HTTP/1.1 specification and supersedes previous headers (e.g. Expires) used to define response caching policies. All modern browsers support Cache-Control, hence that is all we will need.

Upvotes: 25

user3241258
user3241258

Reputation: 535

If you are using a CDN (Cloud Delivery Network) I recommend to use Cache-Control with a max-age time in seconds. For example Cache-Control: max-age=604800. This prevents request-peaks to your origin-server: With "Expires Wed, 30 Oct 20xx 04:37:07 GMT" all browsers will request you at the same time.

Upvotes: 47

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