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Before taking this lesson

Make sure you are comfortable with the following lessons:

  • Introduction to the mabl Test Automation Application
  • Reports: Tests, Plans, Workspaces

Learning Objectives 🧠

By the end of this you will:

  • Understand the basics of performance insights in mabl
  • Know how to download performance data
  • Understand what a “Speed Index” is and how it relates to performance
  • Explore ways to use performance data to investigate any changes in speed index over time

Why is performance important? 

  • Performance metrics give you valuable insight into what experience your customers or users have when they’re navigating around your application. Is your application loading quickly? Or are users getting frustrated with long wait times? Leveraging performance data, your team can take steps to optimize the speed index and improve the overall user experience. 
  • Performance data in your mabl test output can help you pinpoint any possible performance regressions in your application. 


Performance data is only available for test runs in Chrome today. 

What is it?

  • Speed index is how your end users experience the load speed of your application. It tracks the application’s page load performance, measured in seconds. The goal is a low score (like when you’re playing golf!). 

Speed index (in seconds)

Interpretation of score





Over 5.8



Learn more about speed index here

  • Mabl captures the step trace to give us access to the speed index and automatically calculates this performance metric. You can view this performance data in a few different ways:
    • Monitor performance across your application in the release coverage dashboard
      • Enterprise users can access this dashboard which includes the average application load time. You can filter for a specific date range and/or for a specific environment.
      • Navigate to Coverage then scroll down to view Average app load time.

  • View test or flow performance over time 
    • On the Performance tab of any user-created mabl test or flow, you can view the cumulative app load time for that particular test/flow over the past 90 days. 
  • View individual test step performance
    • On the output view of the test run, navigate to the Logs tab and then Performance. Here you’ll see the speed index chart for that particular step. This chart shows the speed index for the test run you’re viewing along with all recent runs of the same test step. 

How can I use mabl’s performance data?

Getting started

Let’s start by exploring performance over time for one of our applications. Select the browser test (reminder: it must be run in Chrome) from the Tests tab, then navigate to the Performance tab. In the upper right corner you can filter for a specific environment if you’d like.

To view more information for a specific date, hover over that date to reveal a tooltip. 

Maybe you find a particular date that you’d like to investigate deeper (because of an uptick in speed index or a significant drop perhaps). Keep that date in mind, then navigate to the Run history tab. Select the test run from that particular date and you’ll view step by step test output data here. 

When you select a test step, you can view Logs and then navigate to the Performance tab. 

Other insight to consider

If there was a change in speed index on a particular day, you can investigate if the team made a change to test coverage. Navigate to the Activity Feed (under Settings > Activity Feed) to see activity in your workspace. You can filter for a specific date. 

Downloading the step trace for further exploration

Under the Actions dropdown in the upper right corner, download the step trace. This will start a JSON file download. Once the file download is complete, you can drag and drop the file into Chrome dev tools to start a deeper investigation on the performance of your application. 

Note: the step trace in Chrome devtools is useful to see how the page acted during the step. Hover over the timeline to see screenshots. 

Viewing the step trace in the Chrome browser

  • Open Chrome dev tools (inspect the page)
  • Navigate to the Performance tab
  • Drag and drop the step trace download (JSON file) on the Performance tab. You can explore from here!
  • Looking for more? View our help guide for downloading performance data



We learned:

  • Speed index measures the application’s page load performance and helps you understand how your end users experience the load speed of your application. The lower the score, the better. 
  • How to investigate performance over time in mabl on the Performance tab of any user-created test. Or dig into performance in individual test steps via the Logs tab in test output. 
  • How to download and use the step trace from mabl in Chrome devtools to explore your application performance and identify any possible regressions.

What to do from here

Explore performance data across your applications! If you spot a regression when viewing performance over time, explore test output data and download the step trace to investigate further in Chrome dev tools.