What is the default screen size for Webpagetest’s Amazon Agents?

Webpagetest, when used in a custom instance on Amazon, can load pre-made on-demand Agents using custom Amazon machines. It is not very clear, however, at what screen size their browsers operate. Apparently, this is kept to a minimum to reduce resource usage, however if you’re testing a website you might need to know at what size the screen is running, for example to check what images are being loaded.

Obviously you can script tests and force screen sizes, like this:

setViewportSize	1366	   768
navigate	https://www.example.com

But I still wanted to know what the default size is. I looked for this information everywhere and I could not find it, so I did a couple of tests against a page on our servers, where JavaScript was outputting the screen dimensions and the inner width of the window, basically this code:

document.getElementById('test').innerHTML = `Screen: ${window.screen.width}   x   ${window.screen.height} <br>     Inner:  ${window.innerWidth} x ${window.innerHeight}     `

The result was, for a Windows agent:

Screen and window inner sizes under Windows

And using a Linux Agent:

Screen and window inner sizes for a Linux agent

This means that, if you have set your standard desktop breakpoint from tablet landscape and above (> 1024px ), like we often do, on a Windows agent you won’t get the desktop layout in the screenshots, but probably the layout you set up for mobile or tablet portrait. Which is the reason why I tested to begin with.

This is it. Thanks for your time, if you find this info useful you can thank me for my time in the comments. Or just clap.

Mioni out.

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