What Does \'?d=20090107\' in a CSS Link Actually Do?

What's the Purpose of '?d=20090107' in CSS Links?

While exploring the HTML of a website, you may come across a filename in this format:

<link href="/Content/all.min.css?d=20090107" rel="stylesheet" type="text/css" />

The mysterious "?d=20090107" appends to the end of the CSS filename. What, exactly, is its function?

Unveiling the Truth

Surprisingly, "?d=20090107" is not a timestamp, as it may initially appear. Instead, it's there to ensure that when the CSS file changes, every client reloads the latest version and doesn't rely on a cached copy.

How the Webserver Handles It

The webserver upon receiving this request ignores the added parameter "?d=20090107" and serves "/Content/all.min.css" as usual.

Why is This Done?

Web developers typically use this method to force a reload of CSS files because it's easier than changing the filenames manually. This is especially helpful when a build or management process tags the files with version numbers.

Alternative Solution

As an aside, you may also encounter the use of Expires or Cache-Control HTTP headers to specify expiration dates for cached files. While this saves unnecessary browser requests, you do risk stale content if the file is changed and the header is not updated accordingly.

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