Track the Impact of Third Party Scripts, Total Blocking Time and More

Karolina Szczur

Karolina Szczur

October 10, 2019

Release Notes is a monthly summary of new features and product improvements.

Analyse the impact of Third Parties

JavaScript continues to be the most performance costly resource, especially if it’s not our code57% of script execution time across the top 4 million sites comes from external sources. Controlling and optimising execution of third parties can be tricky, and in some cases, impossible.

That’s why the transparency of the impact additional tools have on user experience is crucial. With reliable data at hand, we can make informed decisions on whether given tools are worth the performance drawbacks. We can audit the services we use—remove, optimise or find alternatives.

You can now learn everything about external scripts under the Third Party tab available for each Snapshot.

Calibre Third Party scripts tab

Calibre provides new metrics, such as:

  • Number of Third Party Providers
  • Transfer Size of Third Parties
  • Main Thread Execution Time of Third Parties

You can add them to your Pulse pages and set budgets against them. Each third party script is grouped by a category, i.e. customer success or analytics. The percentage of Total Page Transfer Size and Main Thread Execution Time is also readily available in the report.

Analysing third party script is a powerful strategy, no matter which industry your product resides in. Calibre now makes it easy for you to uncover which tools bring you the most trouble.

Block specific Third Parties in Test Profiles

With the release of Third Party tracking, you can now create new Test Profiles tracing performance while blocking selected external scripts:

Calibre Third Party Test Profiles

A few good examples of Test Profiles to establish would be disabling:

  • chat widgets and communication tools
  • scripts providing polyfills
  • analytics software
  • bug tracking

The difference in metrics when enabling those profiles can be quite prounced:

Calibre Third Party Test Profiles compared

Improved Test Verification and Metric Budgets notifications

We’re always working on advancing the reliability of our metrics. Previously, we automatically re-run tests showing significant spikes compared to previous results. Now, we compare to the median of the last three runs and use a grading curve to confirm if the change indeed has to be verified.

Additionally, we now run multiple tests to verify Metric Budget status change. Before you receive a budget notification, we’ll make sure it was met or blown.

New metric: Total Blocking Time

Total Blocking Time (TBT) is an experimental, new metric coming from Google Lighthouse. TBT reflects the time between First Contentful Paint and Time to Interactive if queuing for any JavaScript task takes longer than 50ms. Alongside TTI, it’s another metric helping to grasp main thread congestion.

You can add Total Blocking Time to the Pulse page through customising the Metric History view and set budgets against it.

Karolina Szczur

Karolina Szczur

Karolina is the Product Design Lead at Calibre. With years of design experience under her belt, she’s responsible for the comprehensive user experience spanning over product, visuals and content. Find her on Twitter or LinkedIn.


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