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Editorial Team
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Asked: 2026-06-07T09:48:38+00:00

I have seen on various sites a querystring followed by a numbers for images

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I have seen on various sites a querystring followed by a numbers for images and css files. When I look at the source code (via Chrome Developer), the cached css files and images do not have the number in the query string in their names. I have also seen on sites where the number changes in the querystrings when I refresh the page.

As example:

myimage.jpg?num=12345

myStyles.css?num=82943

After refresh:

myimage.jpg?num=67948

myStyles.css?num=62972

Can anyone explain to me what could possibly be the purpose of these querystrings short of tracking?

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1 Answer

  1. Editorial Team

    Often times developers use those query strings with random numbers (or version numbers) to force the browser to request a fresh copy and avoid caching of those files since the request is different each time.

    So if you have a file /image.png but it is a generated image, like perhaps a captcha or something, you could follow it with a random number querystring /image.png?399532 which the browser would then not pull image.png from its cache, but instead will download a fresh copy from the server.

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