I looked it up and as it turns out, their flush caching facility is not available to me in the wordpress dashboard as it is a subdirectory /wp/ installation. This page was last modified on Jul 4, 2025 by MDN contributors. Must-understand should be coupled with no-store for fallback behavior.
When you build static assets with versioning/hashing mechanisms, adding a version/hash to the filename or query string is a good way to manage caching. No-cache allows clients to request the most up-to-date response even if the cache has a fresh response. When you use a cache-busting pattern for resources and apply them to a long max-age, you can also add immutable to avoid revalidation.
- This section lists directives that affect caching — both response directives and request directives.
- The React library version will change when you update the library, and hero.png will also change when you edit the picture.
- In such a case, you could address the caching needs by using a specific, numbered version of the library, and including the hash of the picture in its URL.
- This page was last modified on Jul 4, 2025 by MDN contributors.
- You can add a long max-age value and immutable because the content will never change.
- The proxy-revalidate response directive is the equivalent of must-revalidate, but specifically for shared caches only.
Response Directives
Use a no-cache to make sure that the HTML response itself is not cached. No-cache could cause revalidation, and the client will correctly receive a new version of the HTML response and static assets. The React library version will change when you update the library, and hero.png will also change when you edit the picture. If you don’t want a response stored in caches, use the no-store directive. For example, a request with the header above indicates that the browser will accept a stale response from the cache that has expired within the last hour.
immutable
- Must-revalidate is a way to prevent this from happening – either the stored response is revalidated with the origin server or a 504 (Gateway Timeout) response is generated.
- If a cache doesn’t support must-understand, it will be ignored.
- If a cache has a stored response, even a stale one, it will be returned.
- If the response becomes stale, it must be validated with the origin server before reuse.
- No-transform indicates that any intermediary (regardless of whether it implements a cache) shouldn’t transform the response contents.
HTTP allows caches to reuse stale responses when they are disconnected from the origin server. Must-revalidate is a way to prevent this from happening – either the stored response is revalidated with the origin server or a 504 (Gateway Timeout) response is generated. The must-revalidate response directive indicates that the response can be stored in caches and can be reused while fresh. If the response becomes stale, it must be validated with the origin server before reuse. Cache that exists between the origin server and clients (e.g., Proxy, CDN). It stores a single response and reuses it with multiple users — so developers should avoid storing personalized contents to be cached in the shared cache.
In the browser, I get a cached version of the stylesheet which does not reflect the recent one. Also, there is no setting to enable “development mode” which apparently turns off caching on the godaddy control panel. Many browsers use this directive for reloading, as explained below.
In such a case, you could address the caching needs by using a specific, numbered version of the library, and including the hash of the picture in its URL. Note that the major browsers do not support requests with max-stale. After the stale-if-error period passes, the client will receive any error generated. If no request happened during that period, the cache became stale and the next request will revalidate normally. Revalidation will make the cache be fresh again, so it appears to clients that it was always fresh during that period — effectively hiding the latency penalty of revalidation from them. This Express middleware sets some HTTP response headers to try to disable client-side caching.
private
Imagine that clients/caches store a fresh response for a path, with no request flight to the server. Clients can use this header when the origin server is down or too slow and can accept cached responses from caches even if they are a bit old. The stale-while-revalidate response directive indicates that the cache could reuse a stale response while it revalidates it to a cache. The proxy-revalidate response directive is the equivalent of must-revalidate, but specifically for shared caches only. If you want caches to always check for content updates while reusing stored content, no-cache is the directive to use.
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Usually, the revalidation is done through a conditional request. Adding no-cache to the response causes revalidation to the server, so you can serve a fresh response every time — or if the client already has a new one, just respond 304 Not Modified. The stale-if-error request directive indicates that the browser is interested in receiving stale content on error from any intermediate server for a particular origin.This is not supported by any browser (see Browser compatibility). Clients can use this header when the user requires the response to not only be fresh, but also requires that it won’t be updated for a period of time.
Caching headers are unreliable in meta elements; for one,any web proxies between the site and the user will completely ignorethem. You should always use a real HTTP header for headers such asCache-Control and Pragma. Note that the major browsers do not support requests with min-fresh. No-transform indicates that any intermediary (regardless of whether it implements a cache) shouldn’t transform the response contents. If a cache doesn’t support must-understand, it will be ignored. Note that s-maxage or must-revalidate also unlock that restriction.
The no-cache request directive asks caches to validate the response with the origin server before reuse. The mining benchmark tool must-understand response directive indicates that a cache should store the response only if it understands the requirements for caching based on status code. If a request doesn’t have an Authorization header, or you are already using s-maxage or must-revalidate in the response, then you don’t need to use public. The no-store response directive indicates that any caches of any kind (private or shared) should not store this response.
The list is just examples of different techniques, it’s not for directinsertion. If copied, the second would overwrite the first and thefourth would overwrite the third because of the http-equivdeclarations AND fail with the W3C validator. At most, one could haveone of each http-equiv declarations; pragma, cache-control andexpires. These are completely outdated when using modern up to date browsers.After IE9 anyway. Chrome and Firefox specifically does not work with these as you would expect, if at all.
See answer here: How to control web page caching, across all browsers?
If a cache supports must-understand, it stores the response with an understanding of cache requirements based on its status code. This section lists directives that affect caching — both response directives and request directives. You can add a long max-age value and immutable because the content will never change.
The public response directive indicates that the response can be stored in a shared cache. Responses for requests with Authorization header fields must not be stored in a shared cache; however, the public directive will cause such responses to be stored in a shared cache. Cache storage isn’t required to remove stale responses immediately because revalidation could change the response from being stale to being fresh again.
The client indicates that an already-cached response should be returned. If a cache has a stored response, even a stale one, it will be returned. If no cached response is available, a 504 Gateway Timeout response will be returned. The no-store request directive allows a client to request that caches refrain from storing the request and corresponding response — even if the origin server’s response could be stored. In general, when pages are under Basic Auth or Digest Auth, the browser sends requests with the Authorization header. This means that the response is access-controlled for restricted users (who have accounts), and it’s fundamentally not shared-cacheable, even if it has max-age.