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Running web performance experiments

DebugBear experiments allow you to run a performance test with modified page HTML.

For example, you can:

  • Remove render-blocking scripts (or make them async)
  • Add or remove preload hints
  • Change the URL of an image

How to run an experiment

  1. Open the results of the page you want to test
  2. Expand the Trigger test now button
  3. Click Run experiment

Run experiment button in sidebar

  1. Provide a name for your experiment, for example "Remove Google Tag Manager"
  2. Edit the HTML document and click Run Experiment

Form with document HTML and name of the experiment

  1. Wait for the test to complete

You can then see the impact of then change. In this example, where Google Tag Manager was removed, for fewer requests were made on the page.

Result of the site speed experiment showing reduced page weight

Interpreting the results of experiments

Your website likely experiences a significant amount of background performance variation. If the performance impact of a change is small, it may not be noticeable.

If your HTML content is large it will load more quickly in an experiment than in a real test. In that case, first run an experiment with no changes to the page and then compare that to the performance experiment.

Document request is broken up into separate round trips normally, but experiment shows only TTFB

Testing private sites or sites that block requests

Loading the initial HTML document for a page may not work if your site requires authentication or blocks bot access. In these cases you can manually paste the page HTML into the text field.