PageSpeed WebPerf Difference Between GTmetrix, PageSpeed Insights, Pingdom Tools & WebPagetest

eva2000 · Aug 3, 2017

GTMetrix folks have posted an article on the differences between pagespeed test results for GTmetrix, PageSpeed Insights, Pingdom Tools & WebPagetest The Difference Between GTmetrix, PageSpeed Insights, Pingdom Tools and WebPagetest

If you’ve used any of these tools, you may wonder why the results are sometimes different. The post serves to highlight the key differences in these performance analysis tools.

We’re glad to be in the company of other great tools that offer an in depth look at website performance.

PageSpeed Insights, Pingdom Tools, and WebPagetest all offer similar features to GTmetrix, but there are a few things that should be pointed out with regards to our differences.
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Time to Stop Test
When each tool decides an analysis is complete will affect your final report.

This is an incredibly important distinction between these tools. Generally speaking, a page analysis can be determined to be complete at two different points, each with their own characteristics:

Onload Time
When the processing of the page is complete and all the resources on the page (images, CSS, etc.) have finished downloading. The browser will trigger window.onload when this occurs.

Issues with using this event: Some elements of the page load may not make it in before this event fires – like JavaScript based image carousels – causing inconsistent page load times and inaccurate screenshots. It may also report faster page load times than actual.

Fully Loaded Time
The point after the Onload event fires and there has been no network activity for 2 seconds. This ensures more consistency with tests.

Possible issues with using this event: This event fires only when a page completely stops loading content, including ads and below the fold elements. Your site might have loaded fast above the fold and be usable, however since the analysis is now waiting for the entire site to stop loading data, your reported Page Load Time might be longer.

Here’s when each tool decides to stop your analysis:

GTmetrix and WebPagetest allow you to switch between Fully Loaded and Onload Time. Pingdom defaults to Onload Time only. This is why you may see Pingdom results loading faster than GTmetrix and/or WebPagetest.

Key Takeaway
Onload time may misrepresent the true load time of your page.

Due to network variances or the way the page was designed to load (eg. asynchronous loading), resources loaded after the browser triggered window.Onload may not make it into reports.

The result is a report that indicates the page loaded faster than it actually did. This means that the while the tool received a “page finished loading” trigger at onload, the actual user is still experiencing resources being downloaded.

This was the key reason why some screenshots were incomplete or page sizes and requests were inconsistent in prior GTmetrix reports.

To make things more consistent, GTmetrix now uses Fully loaded time, which waits for 2 seconds of network inactivity before stopping the test.

Read more about why we switched to Fully Loaded Time here.
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Personally, I find WebPageTest most accurate for my needs

eva2000 · Aug 3, 2017

Explains why newer GTMetrix page speed is longer than before due to such changes New Performance Timings Available / Default to Fully Loaded Time

Tests now defaulted to stop at Fully loaded time
GTmetrix previously used Onload time as the point to stop the test. Due to network variances or the way the page was designed to load (eg. asynchronous loading), resources loaded after the Onload time and not make it into the report, resulting in some pages yielding inconsistent results. Instead, we now wait for 2 seconds of inactivity before stopping the test (what we now call the Fully loaded time).

To explain why, we’ll need to clarify the difference between Onload time and Fully loaded time:

Onload time – is when the processing of the page is complete and all the resources on the page (images, CSS, etc.) have finished downloading.

This used to be the point where GTmetrix would stop the test and mark as the Page Load Time in the GTmetrix report.

Issues with using this event: Some elements of the page load may not make it in before this event fires – like JavaScript based image carousels – causing inconsistent page load times and inaccurate screenshots.

Fully loaded time – is the point after the Onload event fires and there has been no network activity for 2 seconds.

Essentially, GTmetrix is now waiting until your page stops transferring data before completing a test, resulting in more consistent page load times

Possible issues with using this event: This event fires only when a page completely stops loading content, including ads and below the fold elements. Your site might have loaded fast above the fold and be usable, however since the analysis is now waiting for the entire site to stop loading data, your reported Page Load Time might be longer.

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elargento · Aug 3, 2017

Thet are blamming competitors?

eva2000 · Aug 3, 2017

elargento said: ↑

Thet are blamming competitors?
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? they're just highlighting the differences in measurements.

elargento · Aug 3, 2017

eva2000 said: ↑

? they're just highlighting the differences in measurements.
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I'm not saying they are lying, just they noticed what their competitors do wrong in case of pingdom

eva2000 · Aug 3, 2017

Yeah it's because users like ourselves bring up the question of differences all the time.

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