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Users can keep seeing an old stylesheet because a cache is allowed to reuse the CSS response while it is still fresh. An ETag does not set how long that response stays fresh: it helps a browser or other cache check whether a stored response has changed when validation is needed. The most reliable way to deploy static CSS is to give changed files new, content-versioned URLs and update the HTML or manifest that references them.
Why a new deployment can still serve last week’s CSS
When a stylesheet stays at the same URL, such as /site.css, a browser or shared cache may already have a stored response for that address. If its freshness lifetime has not expired, the cache can reuse the response without contacting the origin server. Changing the file on the server does not by itself tell caches that the representation at that URL has changed. RFC 9111 explains that a fresh response can satisfy later requests without contacting the origin (RFC 9111, HTTP Caching).
That is why a deployment can be correct at the origin while users still see old styling. The HTML may also continue to point to the previous stylesheet URL, in which case the browser is following the reference it was given.
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What max-age and ETag actually do
max-age sets freshness
Cache-Control: max-age=3600 gives a response a freshness lifetime of 3,600 seconds, subject to HTTP cache age calculations. It is not necessarily 3,600 seconds from the moment a particular user first sees the file: an upstream cache may already have held it, and the Age response header reports time since generation or successful validation. See RFC 9111 and MDN’s Cache-Control reference.
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ETag validates a stored representation
An ETag is an opaque identifier for a particular representation. When a stored response needs validation, a client can send its value in If-None-Match. If the representation has not changed, the server can confirm that without retransmitting the CSS body; if it has changed, the client can receive the updated representation. ETag is a validator, not a freshness timer. MDN describes the header and conditional requests in its ETag reference.
Last-Modified is another validator
Servers can also provide Last-Modified, which clients can use with If-Modified-Since to ask whether a representation has changed since a stated time. ETag and Last-Modified may both be present; they are validation mechanisms, not substitutes for choosing an appropriate freshness policy. See MDN’s HTTP caching guide.
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no-cache is not no-store
Cache-Control: no-cacheallows a response to be stored, but requires validation before it is reused.Cache-Control: no-storeinstructs caches not to store the response.
Use the directive that matches the intended behavior; “no-cache” does not mean “do not save.” The distinctions are documented in MDN’s Cache-Control reference.
Vary can affect which stored response applies
The Vary header identifies request fields that distinguish representations. Under RFC 9111, a cache must not reuse a response containing Vary without revalidation unless the nominated request fields match those from the request that populated the stored response. This matters when different requests can legitimately receive different versions of a resource (RFC 9111).
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Choose a deployment strategy for CSS
| Approach | Freshness and validation | Deployment behavior | Trade-off |
|---|---|---|---|
| Stable URL with revalidation | Keep the URL and use no-cache or a short freshness lifetime with validators such as ETag. |
A later request can validate the stored response against the origin. | Simple URLs, but clients may need a request to discover a change. |
| Content-versioned URL | Give changed content a new URL, then set a long freshness lifetime; immutable can be appropriate when content at that versioned URL will not change. |
Update the HTML or manifest to reference the new asset; old URLs can remain cached. | Efficient reuse of unchanged assets, but the publishing pipeline must update references correctly. |
For example, a build might emit site.8f3a.css and update the page or manifest to point to that filename. The hash is illustrative, not a required format. MDN gives Cache-Control: max-age=31536000, immutable as an example for a versioned resource; it is an example configuration, not a universal freshness recommendation (MDN’s HTTP caching guide).
Whichever strategy you choose, the document that names the asset must itself be reasonably fresh or revalidated. If the HTML keeps referencing the old filename, deploying a new CSS file under a different name will not make the page request it.
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Trace the CSS request in Chrome DevTools
- Inspect the actual request. Open Chrome DevTools, select Network, reload the page, and filter for the stylesheet. Check its request URL, status, response body, and response headers—especially
Cache-Control,Age,ETag, andLast-Modified. Chrome documents searching headers and responses in the Network panel reference. - Confirm the requested version. Compare the URL in Network with the filename expected for the deployment. If it is still the previous version, inspect the HTML or application manifest that supplies the stylesheet reference.
- Isolate the browser HTTP cache. As a diagnostic, select Disable cache in DevTools while it is open, or use DevTools’ documented clear-cache and hard-reload workflows. If the result changes, browser caching is implicated. This does not purge a CDN or alter production response headers. See Chrome’s Network panel reference.
- Check service-worker and application storage. If the response remains unexpected, inspect the Application panel’s service workers and Cache Storage. A service worker can participate in app-level caching, so response headers alone may not explain what the page receives. Chrome documents these controls in its Application panel reference.
- Compare shared-cache behavior. If users in different regions or on different networks get different results, examine the CDN or other shared-cache policy, including its treatment of
Vary. RFC 9111 describes shared-cache behavior, but purge steps depend on the specific service and configuration (RFC 9111).
Why reloads do not always settle the question
Do not assume every navigation or reload gesture has identical cache behavior across browsers. Browser reload and history-navigation behavior can differ, and restoring a page from history may use a snapshot without revalidation. For practical browser caching guidance, see MDN’s HTTP caching guide. Inspecting the actual request and response is more useful than treating a particular reload gesture as proof that every cache layer was bypassed.
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- The requested URL is old: the document or manifest is still referencing the old asset. Fix that reference or ensure the deployed document is being refreshed.
- The URL is stable and the response is fresh: the cache may be correctly reusing it under its freshness policy. Adjust that policy or move to versioned asset URLs.
- The response is stale and validation occurs: check the conditional request and the server’s response. ETag can reduce transfer when content is unchanged, but a changed representation must be delivered.
- DevTools bypasses the browser cache but the page still looks wrong: examine service-worker handling and Cache Storage, then shared caches and their policies.
- Results vary by client or region: compare the URL, response headers, and shared-cache behavior for each path; check whether
Varymatches the representations being served.
HTTP caching separates reuse from change detection: freshness decides whether a stored response may be reused without a request, while validators help determine whether a stored response still matches when validation happens. The IETF states in RFC 9111 §4.2: “When a response is fresh, it can be used to satisfy subsequent requests without contacting the origin server, thereby improving efficiency.”
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