Web

Software Engineering 16 Sep 2026 6 min read

Vary Expands HTTP Cache Selection Beyond the URI

Two GET requests for the same target URI can require different cached responses. If an origin selects representation metadata or content from request headers such as Accept-Encoding, a cache keyed only by the URI can return a representation selected for a different request. HTTP’s Vary response field extends cache selection across nominated request fields. It does not merely document negotiation. For a stored response carrying Vary, those nominated fields constrain whether that response can satisfy a later request without revalidation.

Software Engineering HTTP

Software Engineering 16 Sep 2026 6 min read

ETag Revalidation Separates Cache Freshness From Representation Transfer

An HTTP cache can hold a response that is no longer fresh yet still avoid downloading the representation again. When the stored response carries a usable validator, the cache can send a conditional request and let the origin confirm whether the selected representation has changed. This separates two operations that are often treated as one: checking whether cached state remains valid and transferring a new representation. A successful revalidation can perform the first without performing the second.

Software Engineering HTTP

Tech 12 Sep 2026 5 min read

Browser Cache and Stale Web Files

A website can change on its server while one browser still shows an older image, script, or page response. Opening the same address in another browser may show the new version immediately. That difference often comes from the browser’s HTTP cache, which can reuse stored responses instead of downloading the same bytes again. The browser cache is not simply a folder of files that are either present or absent. HTTP gives cached responses a freshness state and provides validators that can check whether stored content still matches the server. Those rules determine when reuse avoids a network transfer and when the browser has to contact the server again.

Browsers Web

Tech 09 Sep 2026 8 min read

Why a Webpage Can Still Look Old After You Refresh It

You know a website has changed, but your browser still shows the old logo, an earlier image, or styling that should have disappeared. You press refresh, yet the page still does not look right. The usual explanation is caching: keeping a temporary copy of web content so it does not have to be transferred again every time it is needed. Caching makes ordinary browsing quicker and reduces unnecessary data transfer, but it also means that loading a page is not always the same as downloading every part of it again.

Browsers Web