index.md

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title: Cacheable
slug: Glossary/Cacheable
page-type: glossary-definition

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A cacheable response is an HTTP response that can be cached, that is stored to be retrieved and used later, saving a new request to the server. Not all HTTP responses can be cached, these are the following constraints for an HTTP response to be cached:

• The method used in the request is itself cacheable, that is either a {{HTTPMethod("GET")}} or a {{HTTPMethod("HEAD")}} method. A response to a {{HTTPMethod("POST")}} or {{HTTPMethod("PATCH")}} request can also be cached if freshness is indicated and the {{HTTPHeader("Content-Location")}} header is set, but this is rarely implemented. For example, Firefox does not support it (Firefox bug 109553). Other methods, like {{HTTPMethod("PUT")}} or {{HTTPMethod("DELETE")}} are not cacheable and their result cannot be cached.

• The status code of the response is known by the application caching, and it is considered cacheable. The following status code are cacheable: {{HTTPStatus("200")}}, {{HTTPStatus("203")}}, {{HTTPStatus("204")}}, {{HTTPStatus("206")}}, {{HTTPStatus("300")}}, {{HTTPStatus("301")}}, {{HTTPStatus("404")}}, {{HTTPStatus("405")}}, {{HTTPStatus("410")}}, {{HTTPStatus("414")}}, and {{HTTPStatus("501")}}.

• There are specific headers in the response, like {{HTTPHeader("Cache-Control")}}, that prevents caching.

Note that some non-cacheable requests/responses to a specific URI may invalidate previously cached responses on the same URI. For example, a {{HTTPMethod("PUT")}} to pageX.html will invalidate all cached {{HTTPMethod("GET")}} or {{HTTPMethod("HEAD")}} requests to the same URI.

When both, the method of the request and the status of the response, are cacheable, the response to the request can be cached:

GET /pageX.html HTTP/1.1
(…)

200 OK
(…)

A {{HTTPMethod("PUT")}} request cannot be cached. Moreover, it invalidates cached data for request to the same URI done via {{HTTPMethod("HEAD")}} or {{HTTPMethod("GET")}}:

PUT /pageX.html HTTP/1.1
(…)

200 OK
(…)

A specific {{HTTPHeader("Cache-Control")}} header in the response can prevent caching:

GET /pageX.html HTTP/1.1
(…)

200 OK
Cache-Control: no-cache
(…)

See also

• Details about methods and caching are provided in the HTTP specification.

• Description of common cacheable methods: {{HTTPMethod("GET")}}, {{HTTPMethod("HEAD")}}

• Description of common non-cacheable methods: {{HTTPMethod("PUT")}}, {{HTTPMethod("DELETE")}}, often {{HTTPMethod("POST")}}