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Website caching reduces repeated work by reusing a stored response when a later request matches and the response is still usable. A browser cache can do this for one visitor; a shared cache, such as a CDN, can serve suitable responses to many visitors. That can spare your origin server from fetching data and building the same response again. “Thousands” is illustrative here, not a measured reduction or a guarantee.
How does caching reduce requests to your server?
A cache sits between a visitor and your origin—the server that runs your website. It checks whether it has a response matching the incoming request and whether that response can still be reused. On a fresh cache hit, it returns the stored response instead of forwarding the request to the origin. If there is no reusable copy, the cache sends the request onward; the origin responds, and the cache may store that response if the caching rules allow it. MDN’s HTTP caching guide describes this as storing a response associated with a request and reusing it for later requests.
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When a request reaches the origin, the site may need to route it, restore a session, query a database, or render a page. A cache hit can avoid some or all of that repeated handling, depending on what is cached. A fresh hit avoids an origin trip; a response that must be revalidated still contacts the origin, even if the cached body can then be reused.
What is the difference between browser and shared caching?
A browser cache is private to a visitor’s client, so it chiefly avoids repeat downloads for that same visitor. A shared cache—such as a proxy or a CDN—can reuse a suitable response for multiple visitors, reducing the number of requests that need to reach the origin.
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Shared caches can also combine simultaneous identical requests: rather than sending every waiting request separately to the origin, a cache may send one and distribute the resulting response to the others. This can help during a burst of traffic, but the amount of origin work avoided depends on the traffic, cacheability, freshness rules, and configuration. The documentation cited here does not establish a fixed request reduction or benchmark.
How do Cache-Control directives affect reuse?
The HTTP Cache-Control response header tells caches whether and how a response may be stored and reused. The directives below have distinct meanings; MDN’s Cache-Control reference documents their behavior.
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| Directive | Effect | Practical meaning |
|---|---|---|
max-age=N |
Makes a response fresh for the specified number of seconds after generation, subject to age and other applicable rules. | A cache can reuse it while it remains fresh. |
no-cache |
Allows storage, but requires successful validation before reuse. | It does not mean “do not store.” |
no-store |
Instructs caches not to store the request or response. | Use when the response should not be kept by caches. |
private |
Reserves the response for a private cache rather than a shared cache. | Relevant for content personalized to one visitor. |
public |
Can indicate that shared caches may store a response in applicable situations. | It does not make personalized content safe to share. |
Freshness and validation are not the same. A fresh hit can be served without contacting the origin. When a stored response is stale but can be validated, the cache asks the origin whether it can reuse the stored response; this still involves the origin, though the cached body may not need to be downloaded again.
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How does a CDN cache help visitors?
A content delivery network (CDN) places shared caches in distributed data centers, allowing cacheable content to be served nearer to visitors. If a cache has no usable copy, it must fetch the response from the origin. What is cached by default, how long it stays fresh, and how origin headers are handled depend on the provider and the site’s configuration.
For example, Cloudflare says that when Origin Cache Control is enabled, a max-age of 3,600 seconds means it will cache a resource for that period before checking the origin again. That is a Cloudflare-specific example, not a rule for every CDN. Cloudflare also says Cache Rules can augment or override origin directives or default policies. See its Origin Cache Control documentation and Cache getting-started guide for those provider-specific details.
When choosing or configuring a shared cache, check where it serves content, whether a response is private or shared, how freshness and validation work, how old copies can be invalidated or purged, and what happens on cache misses. Confirm that the provider’s current settings honor or override your origin’s headers as intended.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How can shared caching go wrong?
If a shared cache does not account for personalization, it may serve one visitor’s response to another. MDN advises using private for personalized responses that should not be shared. The web.dev security and privacy guidance also explains the risks of HTTP cache misconfiguration.
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Keep account pages, checkout flows, and other user-specific responses out of shared caching unless the implementation explicitly and correctly protects them. A broad public directive does not make such content safe; cache policy and the cache’s request-matching behavior need to fit the response.
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