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In <link rel="stylesheet" href="css/styles.css?v=1.0">, ?v=1.0 is a query component on the stylesheet’s URL. Developers commonly change its value when the CSS file changes so the URL becomes different and browsers or caches are less likely to reuse an older copy. This technique is usually called cache busting.
How to read ?v=1.0
The question mark starts the URL query. In this example, v is a parameter name and 1.0 is its value:
?introduces the query string.vis a developer-chosen parameter name, often meaning “version.”1.0is an arbitrary value supplied with the request.
It is not an HTML attribute, a CSS instruction, or a special version declaration understood by the browser. It is simply part of the resource URL.
Why developers change the value
Browsers and intermediary caches can retain stylesheets. If a site changes styles.css but keeps exactly the same URL, a visitor may temporarily receive a cached copy. Changing the URL, for example from styles.css?v=1.0 to styles.css?v=1.1, gives the request a new URL and is intended to make the updated stylesheet more likely to be requested.
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Other values can serve the same purpose
The value does not have to follow semantic versioning. A timestamp or a build-generated identifier can be used instead, provided it changes when the CSS changes. For example:
styles.css?v=20261002styles.css?v=build-8472
The value itself does not tell the browser how to compare CSS versions; the application or deployment process decides when to change it.
What happens on the server
When the browser requests the URL, the query is sent to the server along with the path. Whether the server, CDN, proxy, or other cache treats different query strings as different resources depends on that system’s configuration. Therefore, changing ?v=1.0 is a cache-busting technique, not a universal guarantee that every layer will fetch fresh content.
Example workflow
- Publish the stylesheet as
css/styles.css?v=1.0. - Edit the CSS file.
- Change the reference to a new value, such as
css/styles.css?v=1.1, or generate a new timestamp or build identifier. - Deploy the HTML and CSS together, then verify the request and response behavior in the target hosting and caching setup.
Important limitation
A December 15–16, 2013 SitePoint forum discussion explains this usage and notes that query-based cache busting may not behave as intended with some proxies or content filters. The exact result depends on the browser, server, CDN, proxy, and cache policy involved, so the example should be understood as a common technique rather than a promise of identical behavior everywhere.
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