Testing a Website from Different Locations Using WebPagetest? Watch Out for This

Strangly, my website seemed to render faster outside of the country it's hosted.

This website is hosted on a German server and I don’t currently use a CDN. So German visitors should be getting the quickest performance timings. But what about my homies in Cali or elsewhere?

I went to WebPagetest and tested a page containing the most resources using “Motorola G (gen 4)” mobile browser emulation and a “3G Fast” connection.

The Page is Rendered Quickest Outside of the Host Country. How Can That Be?

As expected, the time to first byte is shortest in Germany – that’s where I host my site.

WebPagetest Locations Comparison: Time to First Byte

But tests run from three locations outside of Germany (Isreal, San Francisco and Dulles, Virginia) were visually complete before the German test.

WebPagetest Locations Comparison: Filmstrip

In fact, the visual progress of German test was pretty average compared to the other test locations.

WebPagetest Locations Comparison: Visual Progress

Apparently, the test from Dulles, VA was fastest to visually complete.

That seemed odd. If the physical distance between host and client is shortest in Germany, then shouldn’t the page finish rendering the quickest there?

WebPagetest Locations Comparison: Visually Complete

More Bytes Sent to Dulles, VA

Then I had a look at Image Bytes and noticed: way more image bytes were being sent to Dulles, VA.

WebPagetest Locations Comparison: Image Bytes

That’s when I realized:

If you test from “Moto G (gen 4)”, you’re testing on a real device – even if you select Browser Emulation.

WebPagetest advanced settings
WebPagetest Chromium settings

Indeed, when comparing test results from "Moto G (gen 4)” and “Virginia USA - EC2” (both with browser emulation), you see more image bytes are downloaded and an additional image request.

WebPagetest Locations Comparison: Moto G vs. EC2 Bytes
WebPagetest Locations Comparison: Moto G vs. EC2 Requests

And performance timings around the board are better for "Moto G (gen 4)” than “Virginia USA - EC2”.

WebPagetest Locations Comparison: Moto G vs. EC2 Timings

I then compared test results using only device emulation (no real devices) and Bytes and Requests were the same:

WebPagetest Locations Comparison: Moto G vs. EC2 Image Requests

Lessons Learned

Testing my website from around the world using WebPagetest taught me:

  1. When testing from various locations around the world, make sure you use emulation only – no real devices.
  2. Testing on real devices will of course give you more realistic performance timings than on emulated devices, but if you’re using public WebPagetest, the test location is Dulles, VA.

Published: Jan 08, 2020

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